Abstract

People say that R is "object-oriented," but I had not appreciated the underlying details until 2013 or so (after using R for 12+ years)

Now I notice the pattern!

Here's the basic recipe
- estimator function creates data structures (not presentable to humans) and declares that thing to be of a certain class.
- programmer then writes summary and other methods that re-structure the data.
- programmer writes display methods: print, plot, for those revised data structures.
Behind the scene, information is passed around in a relatively ugly format
We show the users a prettied-up version.
Want examples I can explain?
- Look in rockchalk
  - meanCenter, residualCenter, standardize. functions that receive regressions, re-assign their classes.
  - pctable, a newer function discussed next

Clunky to use, too

Compared to other R functions, there is no beauty in the table function.

table(dat$yf1, dat$xf1)

I wanted something that looked more like a regression model

myTable(yf1 ~ xf1, data = dat)

I wanted to replace this style

table(dat$yf1, dat$xf1, dnn = list("My Great Row Var", "My Column Var"))

##                 My Column Var
## My Great Row Var Alberquerque Denver Santa Fe
##                a            5      5        8
##                b           14      9       14
##                c            8     13       15
##                d            5      7       13
##                e           11     11        5

with this:

myTable(yf1 ~ xf1, data = dat, rvlab = "My Great Row Var", cvlab = "My Column Var")

The function tabl (for the NLTS2 project) did about the right thing.

tabl(yf1, xf1, data = dat)

##      xf1
## yf1   Alberquerque Denver    Santa Fe  NA     Sum
##   a   5(11.1%)     5(11.1%)  8(14.3%)  2(50%) 20 
##   b   14(31.1%)    9(20%)    14(25%)   0(0%)  37 
##   c   8(17.8%)     13(28.9%) 15(26.8%) 0(0%)  36 
##   d   5(11.1%)     7(15.6%)  13(23.2%) 0(0%)  25 
##   e   11(24.4%)    11(24.4%) 5(8.9%)   2(50%) 29 
##   NA  2(4.4%)      0(0%)     1(1.8%)   0(0%)  3  
##   Sum 45           45        56        4      150

Declaration like so

tabl <- function(x, y, data = parent.frame(), xlab = NULL, 
                  ylab = NULL, exclude = NULL, rounded = FALSE)

That was not very flexible, but went in good direction
- data frame argument!
- Some argument magic here. Allows users to name symbols as input variables, not quoted variable names "xf1". That gets sacrificed in the sequel.
- Defaults to show missing values

pctable() in the rockchalk package 1.8.90+

Much more flexible
- use a formula interface
```
t1 <- pctable(yf1 ~ xf1, dat)
```
creates a data structure in t1 that can be used to spit out various summaries
- Or even use it the old way
```
pctable(dat$yf1, dat$xf1)
```
- It turns out it is not allowed/practical to have this interface,
```
pctable(yf1, xf1, dat)
```
- However, I found a way to implement this
```
pctable("yf1", "xf1", dat)
```
which is almost as good.
Found ways to export to LaTeX and Word compatible formats, so students can make tables that don't offend the reader
Keep options open to include counts and percents in same table

pctable is pronounced "presentable"

library(rockchalk)
pctable(yf1 ~ xf1, data = dat, rvlab = "A Thing I Predict", cvlab = "A Mighty Predictor!")

## Count (column %)
##                  A Mighty Predictor!
## A Thing I Predict Alberquerque Denver    Santa Fe  Sum
##               a   5(11.6%)     5(11.1%)  8(14.5%)  18 
##               b   14(32.6%)    9(20%)    14(25.5%) 37 
##               c   8(18.6%)     13(28.9%) 15(27.3%) 36 
##               d   5(11.6%)     7(15.6%)  13(23.6%) 25 
##               e   11(25.6%)    11(24.4%) 5(9.1%)   27 
##               Sum 43           45        55        143

In my opinion, nobody should ever want row percents, but if you do, I will still be your friend:

pctable(yf1 ~ xf1, data = dat, rowpct = TRUE, colpct = FALSE)

## Count (row %)
##      xf1
## yf1   Alberquerque Denver    Santa Fe  Sum
##   a   5(27.8%)     5(27.8%)  8(44.4%)  18 
##   b   14(37.8%)    9(24.3%)  14(37.8%) 37 
##   c   8(22.2%)     13(36.1%) 15(41.7%) 36 
##   d   5(20%)       7(28%)    13(52%)   25 
##   e   11(40.7%)    11(40.7%) 5(18.5%)  27 
##   Sum 43           45        55        143

Make a high quality table

	xf1
yf1	Alberquerque	Denver	Santa Fe	NA	Sum
a	5(11.1%)	5(11.1%)	8(14.3%)	2(50%)	20
b	14(31.1%)	9(20%)	14(25%)	0(0%)	37
c	8(17.8%)	13(28.9%)	15(26.8%)	0(0%)	36
d	5(11.1%)	7(15.6%)	13(23.2%)	0(0%)	25
e	11(24.4%)	11(24.4%)	5(8.9%)	2(50%)	29
NA	2(4.4%)	0(0%)	1(1.8%)	0(0%)	3
Sum	45	45	56	4	150

What's required to make this work?

From rockchalk source code, this is it!

pctable <- function(rv, ...)
{
    UseMethod("pctable")
}

pctable.formula <- function(formula, data = NULL,  rvlab = NULL,
                            cvlab = NULL, colpct = TRUE, rowpct = FALSE,
                            rounded = FALSE, ...)
    
{
    if (missing(formula) || (length(formula) != 3L))
        stop("pctable requires a two sided formula")
    mt <- terms(formula, data = data)
    if (attr(mt, "response") == 0L) stop("response variable is required")
    mf <- match.call(expand.dots = TRUE)
    mfnames <- c("formula", "data", "subset", "xlev", "na.action", "drop.unused.levels")
    keepers <- match(mfnames, names(mf), 0L)
    mf <- mf[c(1L, keepers)]
    ## mf$drop.unused.levels <- FALSE
   
    mf[[1L]] <- quote(stats::model.frame)
    dots <- list(...)
    ## remove used arguments from dots, otherwise errors happen
    ## when unexpected arguments pass through. Don't know why
    for (i in c("subset", "xlev", "na.action", "drop.unused.levels")) dots[[i]] <- NULL
        
    mf <- eval(mf, parent.frame())
    mfnames <- names(mf)
    response <- attr(attr(mf, "terms"), "response")
    ## response is column 1
    rvname <- mfnames[response]
    cvname <- mfnames[-response][1] ##just take 2?
    rvlab <- if (missing(rvlab)) rvname else rvlab
    cvlab <- if (missing(cvlab)) cvname else cvlab

    arglist <- list(rv = mf[[rvname]], cv = mf[[cvname]],
                    rvlab = rvlab, cvlab = cvlab,
                    colpct = colpct, rowpct = rowpct,
                    rounded = rounded)
    arglist <- modifyList(arglist, dots, keep.null = TRUE)
    ##keep.null needed because exclude = NULL can be a valid
    ## (meaningful) argument to table.
    
    res <- do.call(pctable.default, arglist)
    invisible(res)
}

pctable.character <- function(rv, cv, data = NULL, rvlab = NULL,
                              cvlab = NULL, colpct = TRUE,
                              rowpct = FALSE,
                              rounded = FALSE, ...)
{
    if (missing(data) || !is.data.frame(data)) stop("pctable requires a data frame")
    cv <- as.character(substitute(cv))[1L]
    
    rvlab <- if (missing(rvlab)) rv else rvlab
    cvlab <- if (missing(cvlab)) cv else cvlab
    res <- pctable.formula(formula(paste(rv, " ~ ", cv)), data = data,
                           rvlab = rvlab, cvlab = cvlab, colpct = colpct,
                           rowpct = rowpct, rounded = rounded, ...)
  
    invisible(res)
}

pctable.default <- function(rv, cv,
                            rvlab = NULL, cvlab = NULL,
                            colpct = TRUE, rowpct = FALSE,
                            rounded = FALSE, ...)
{
    rvlabel <- if (!missing(rv)) deparse(substitute(rv))
    cvlabel <- if (!missing(cv)) deparse(substitute(cv))
    rvlab <- if (is.null(rvlab)) rvlabel else rvlab
    cvlab <- if (is.null(cvlab)) cvlabel else cvlab

    dots <- list(...)
    dotnames <- names(dots)
    ## altargs <- list()
   
    ## if ("dnn" %in% dotnames) altargs$dnn <- dots[["dnn"]]
    ## if ("deparse.level" %in% dotnames)
    ##     altargs$deparse.level <- dots[["deparse.level"]]
    
    tableargs <- list(rv, cv, dnn = c(rvlab, cvlab))
    newargs <- modifyList(tableargs, dots, keep.null = TRUE)

    t1 <- do.call("table", newargs)
    rownames(t1)[is.na(rownames(t1))] <- "NA" ## symbol to letters
    colnames(t1)[is.na(colnames(t1))] <- "NA"
    if (rounded) t1 <- round(t1, -1)
    t2 <- addmargins(t1, c(1,2))
    t1colpct <- round(100*prop.table(t1, 2), 1)
    t1rowpct <- round(100*prop.table(t1, 1), 1)
    t1colpct <- apply(t1colpct, c(1,2), function(x) gsub("NaN", "", x))
    t1rowpct <- apply(t1rowpct, c(1,2), function(x) gsub("NaN", "", x))
    res <- list("count" = t2, "colpct" = t1colpct, "rowpct" = t1rowpct,
                call = match.call())
    class(res) <- "pctable"
    print.pctable(res, colpct = colpct, rowpct = rowpct)
    invisible(res)
}


print.pctable <- function(x, colpct = TRUE, rowpct = FALSE, ...)
{
    colpct <- if (missing(colpct)) x$call[["colpct"]] else colpct 
    rowpct <- if (missing(rowpct)) x$call[["rowpct"]] else rowpct
    tab <- summary(x, colpct = colpct, rowpct = rowpct)
    print(tab, ...)
    invisible(tab)
}

summary.pctable <- function(object, ..., colpct = TRUE, rowpct = FALSE)
{
    colpct <- if (missing(colpct)) object$call[["colpct"]] else colpct 
    rowpct <- if (missing(rowpct)) object$call[["rowpct"]] else rowpct
    
    count <- object[["count"]]
   
    t3 <- count
    attr(t3, which = "colpct") <- colpct
    attr(t3, which = "rowpct") <- rowpct
    class(t3) <- c("summary.pctable", "table")
    if (colpct && !rowpct) {
        cpct <- object[["colpct"]]
        for(j in rownames(cpct)){
            for(k in colnames(cpct)){
                t3[j, k] <- paste0(count[j, k], "(", cpct[j, k], "%)")
            }
        }
        return(t3)
    }
    
    ## rowpct == TRUE else would have returned
    rpct <- object[["rowpct"]]
    for(j in rownames(rpct)){
        for(k in colnames(rpct)){
            t3[j, k] <- paste0(count[j, k], "(", rpct[j, k], "%)")
        }
    }
    
    if (!colpct) {
        return(t3)
    } else {
        cpct <- object[["colpct"]]
        t4 <- array("", dim = c(1, 1) + c(2,1)*dim(object$colpct))
        t4[seq(1, NROW(t4), 2), ] <- t3
        rownames(t4)[seq(1, NROW(t4), 2)] <- rownames(t3)
        rownames(t4)[is.na(rownames(t4))] <- "" 
        colnames(t4) <- colnames(t3)
        for(j in rownames(object[["colpct"]])) {
            for(k in colnames(object[["colpct"]])){
                t4[1 + which(rownames(t4) == j) ,k] <- paste0(object[["colpct"]][j, k], "%")
            }
            
        }
        t4 <- as.table(t4)
        names(dimnames(t4)) <- names(dimnames(count))
        attr(t4, which = "colpct") <- colpct
        attr(t4, which = "rowpct") <- rowpct
        class(t4) <- c("summary.pctable", "table")
        return(t4)
    }
}

print.summary.pctable <- function(x, ...){
    colpct <- attr(x, "colpct")
    rowpct <- attr(x, "rowpct")
    
    if (colpct && !rowpct) {
        cat("Count (column %)\n")
    } else if (!colpct && rowpct) {
        cat("Count (row %)\n")
    } else {
        cat("Count (row %)\n")
        cat("column %\n")
    }
    NextMethod(generic = "print", object = x, quote = FALSE, ...)
}

pctable is designed with the R secret recipe in mind.

pctable creates a set of data structures
summary.pctable can create a summary view, which picks through the structures to make the desired information.
print.summary.pctable displays the summary to the user

Same sequence plays itself out across the R source code

User runs a model-making function

m1 <- lm(y1 ~ xf1 + x2, data = dat)

R "knows what to do" when we pass m1 is used as an argument to other functions. We run

summary(m1)

plot(m1)

Results come not from functions named summary, or plot, but rather from functions named summary.lm or plot.lm. Those special, class-specific functions are called methods

Attributes

m1 has an attribute named "class", which is set to the value of "lm".
R runtime system depends on the class attribute.
- See all attributes
```
attributes(m1)
```
- Or just the one attribute we want to know
```
class(m1)
```

R Functions set Attributes as class strings.

Check any of the major model fitting functions in the R source code.

They build up a list of results (estimates, other record-keeping elements).
They then set attributes on that list
Toward the end, as in the lm() function, one will find:

class(z) <- c(if (is.matrix(y)) "mlm", "lm")

If the model is multivariate, the class vector will be c("mlm", "lm"), otherwise just "lm".
More specialized classes are appended on the front of the list.
Something classed as c("mlm", "lm") can have specialized functions for "mlm" objects where needed, but can use functions intended for "lm" objects when suitable.

The S3 system is very informal

Can set class attribute to anything you want
Unlike more structured languages like C++ or Java, there is no type-checking to make sure this makes sense.
No need to "register" the class with the runtime system in any more elaborate way.
For existing R generic functions like summary, plot, print, table, and so forth, one need only create functions named summary.mynewclass, print.mynewclass, table.mynewclass, etc.

Create some mischief, version 1.

If you lie to the R runtime by claiming something is an instance of something else, then you generally get errors that seem somewhat opaque.

m1 <- c(1, 2, 3)
class(m1) <- "lm"
> summary(m1)

Error: $ operator is invalid for atomic vectors

Create some mischief, version 2

Here's a real lm regression object

m1 <- lm(y ~ xf1, data = dat)

Add a new class on the front.

class(m1) <- c("pjgreatest", class(m1))
class(m1)

## [1] "pjgreatest" "lm"

The "pjgreatest" class has no methods, so anything we run will "still work" because R looks at the class list. It finds no method "summary.pjgreatest", but it finds the Next Method "summary.lm". See?

summary(m1)

## 
## Call:
## lm(formula = y ~ xf1, data = dat)
## 
## Residuals:
##    Min     1Q Median     3Q    Max 
## -2.924 -0.736  0.186  0.617  2.567 
## 
## Coefficients:
##             Estimate Std. Error t value Pr(>|t|)
## (Intercept)    0.117      0.151    0.77     0.44
## xf1Denver      0.113      0.214    0.53     0.60
## xf1Santa Fe   -0.244      0.203   -1.20     0.23
## 
## Residual standard error: 1.02 on 143 degrees of freedom
##   (4 observations deleted due to missingness)
## Multiple R-squared:  0.0225, Adjusted R-squared:  0.00887 
## F-statistic: 1.65 on 2 and 143 DF,  p-value: 0.196

Now lets provide a new summary method

summary.pjgreatest <- function(object, ...){
    newres <- NextMethod(generic = "summary", object = object, ...)
    newres$Rsquare <- runif(1, min = 0.90, max = 0.999)
    class(newres) <- c("summary.pjgreatest", class(newres))
    newres
}

The strong (strong!) recommendation from the R developers is to write summary methods that return data structures, and then we write a print method to display that structure.

print.summary.pjgreatest <- function(x, ...){
    cat("You are now in the twilight zone. \n")
    cat("All regressions fitted here are nearly perfect. \n")
    cat(paste("The Rsquare is", x$Rsquare, "\n\n"))
    cat(paste("That's a great Rsquare, just like you deserve! \n\n"))
    cat("But if you want to believe those R guys, the R square is only", x$r.square, "\n\n")
    cat("See?\n")
    NextMethod(generic = "print", object = x,  ...)
}

summary(m1)

## You are now in the twilight zone. 
## All regressions fitted here are nearly perfect. 
## The Rsquare is 0.993479372466216 
## 
## That's a great Rsquare, just like you deserve! 
## 
## But if you want to believe those R guys, the R square is only 0.02255 
## 
## See?
## 
## Call:
## lm(formula = y ~ xf1, data = dat)
## 
## Residuals:
##    Min     1Q Median     3Q    Max 
## -2.924 -0.736  0.186  0.617  2.567 
## 
## Coefficients:
##             Estimate Std. Error t value Pr(>|t|)
## (Intercept)    0.117      0.151    0.77     0.44
## xf1Denver      0.113      0.214    0.53     0.60
## xf1Santa Fe   -0.244      0.203   -1.20     0.23
## 
## Residual standard error: 1.02 on 143 degrees of freedom
##   (4 observations deleted due to missingness)
## Multiple R-squared:  0.0225, Adjusted R-squared:  0.00887 
## F-statistic: 1.65 on 2 and 143 DF,  p-value: 0.196

Generic Functions

Definition: a function that receives a request and sends it to another function

Generic usage

summary(m1)

calls a method (an R function) named summary.lm

"Dispatching" in S3. R runtime looks at the class of the FIRST input argument, and then sends the work to the other function.
I learned the importance of this when working on pctable. It's possible to
- write a formula method pctable.formula, so users can run pctable(y ~ x, data = dat)
- write a character method pctable.character, so users can run pctable("y", "x", data = dat)
- but it is not possible to write a method in which the first argument is nothing, such as pctable(y, x, dat) because y does not exist and the S3 dispatcher becomes hopelessy confused.

Generic functions almost always are simple with a minimal declaration

"..." is a legal word. Meaning "user can add named arguments and if they don't match the ones we expect, we'll toss all of them into "...". Comments about processing "..." included in new Rchaeology.
The generic print

print <- function(x, ...) UseMethod("print")

This preserves flexibility, puts weight of work onto methods, which
- can have more named arguments.
- must have arguments x and ...

Generic functions

Examples of commonly used generics
- summary, print, plot
Methods examples
- summary.lm (creates new object with class "summary.lm")
- summary.glm
- summary.table
R has tools to see methods that are available
- list available print methods
```
methods(print)
```
- list methods that can apply to objects of class "lm"
```
methods(class = "lm")
```

Methods

Method is the name for those "other functions" that actually do the work.
Named in format "generic.class".
If the class attribute of x is c("A","B"), then print(x) looks for
- print.A Not finding that, it looks for print.B
- Not finding that, it looks for print.default
- summary.class should always create a new object, the class of
- which is summary.class and the print method for that
- would be named print.summary.class

print methods

print.table <- function (x, digits = getOption("digits"), 
                           quote = FALSE, na.print = "",
                           zero.print = "0", justify = "none", ...)

print.lm <- function (x, digits = max(3L, getOption("digits") - 3L), ...)

print.default <- function(x, digits = NULL, quote = TRUE, na.print = NULL,
                          print.gap = NULL, right = FALSE, max = NULL,
                          useSource = TRUE, ...)

print methods usually have to be separately created for the class and all of its derivative subclasses
- print.lm
- print.summary.lm

... is a three letter word

Literally, the period is a legal character, three periods is a word!
There's not much manual info on "...". I have found the only solution was a careful study of the R source code. See how they do it, then do it like they do.
Explanation inserted into new Rchaeology vignette. Will get better
Inside a function, we almost always either grab and inspect the dots

dots <- list(...)
dotnames <- names(dots)

Often, the dots have argument that are intended for a particular purpose. We often have to separate the arguments, by name (dotnames).

S3/S4

S4 is a more elaborate object structure, more formal, less prone to mischief of the sort we just explored.
Seems that many packges, and almost all of base R, are still written in S3.
The fact that the 2 sorts coexist in the same runtime causes a lot of trouble for me.
- Different accessors.
  - S3 uses dollar signs, dat$x same as dat[ , "x"]
  - S4 uses @ as accessor.
So function receives an object, we have to write specialized code to figure out if the thing is S3 or S4 and then use $ and @ properly.

Building an S3 class around an Mplus Automation result

If you've never done this, you should try it.

Let your GRAs write functions however they want to, without enforcing any naming scheme or style. Let them accumulate a few 1000 lines.
Then tell them that you want to hide all of that detail in a package and expose to the users only a simple set of standard-looking functions.

m1 <- fitter(y ~ x1 + x2, data = dat)
summary(m1)
coef(m1) ## method displays brief 
coef(summary(m1)) ## makes parameter table
anova(m1)
plot(m1)

I say you should try that because it is fun to watch the complaining

We began with an interace with idiosyncratic names like

runEverything <- function(dFrame = NULL, formString = NULL,
                          missValue = -999, patternV = patternVector,
                          mScript = mplusSkel, mplusFile = 'mplus.csv',
                          isMissing = FALSE, numPerLine = 5, isWeighted = FALSE,
                          mplusDir = "../../NLTS2-data/Mplus/", subPop = FALSE)

summarizeObj <- function(List = NULL, r.VGAM = FALSE, dFrame = NULL)

Here's what we end up with

stages <- function(formula = NULL, data = NULL,
                   missValue = -999, skel = mplusSkel,
                   mplusFile = 'mplus.csv',
                   isMissing = FALSE, numPerLine = 5, isWeighted = FALSE,
                   mplusDir = "../../NLTS2-data/Mplus/", subPop = FALSE)
{
    require(MplusAutomation)
    if (!file.exists(mplusDir)) dir.create(mplusDir, showWarnings = FALSE, recursive = TRUE)
    if (!plyr::is.formula(formula)) formula <- as.formula(formula)

    ## Create the matrix and recoding for Mplus
    mMat <- makeMplusMat(formula, data, missValue)

    ## Make the number of stages
    nstages <- length( unique( mMat[mMat[, 1] != -999, 1] ) )
    ## Check if nstages is 2, 3, or 4
    if(nstages < 2 || nstages > 4){
        stop('The number of stages must be 2, 3, or 4')
    }

    ## Add in code about 2 stages aka logistic regression
    if(nstages > 2){
        mMat <- recodeMplus(mMat, nstages, missValue)
    }

    ## Makes the replacement vector along with the mplus Key for conversion later returns list
    rList <- makeReplacementVector(mplusFile = mplusFile,
                                   data = mMat,
                                   skel = skel,
                                   isMissing = isMissing,
                                   numPerLine = numPerLine,
                                   isWeighted = isWeighted,
                                   nstages = nstages,
                                   missValue = as.character(missValue),
                                   subPop = subPop)
    mplusKey <- rList[[2]]

    outList <- runMplus(data = mMat, replaceV = rList[[1]], skel,  mplusDir, mplusFile)

    ## more direct way to rename all values in param column, misses Thresholds, however
    pjkey <- mplusKey[ , "predictors"]
    names(pjkey) <- mplusKey[ , "mplus"]

    ## Now beautify names of variables and columns in parameter objects
    newheaders <- c(pval = "Pr(>|z|)", est = "Estimate", se = "Std Error", est_se = "z value")
    for(aname in names(outList$parameters)){
        param <-  outList[["parameters"]][[aname]][["param"]]
        outList[["parameters"]][[aname]][["param"]] <- 
                 ifelse( param %in% names(pjkey), pjkey[param], param)
        ## PJ. need to catch thresholds named V$x. make second pass
        param <- sapply(strsplit(param, "\\$"), function(xxx) xxx[1])
        outList[["parameters"]][[aname]][["param"]] <- 
                 ifelse( param %in% names(pjkey), pjkey[param], param)

        paramHeader <-  outList[["parameters"]][[aname]][["paramHeader"]]
        phlist <- strsplit(paramHeader, "\\.")
        for(i in seq_along(phlist)){ phlist[[i]][1] <- ifelse(phlist[[i]][1] %in% names(pjkey),
                                                              pjkey[phlist[[i]][1]],
                                                              phlist[[i]][1])
                                 }

        outList[["parameters"]][[aname]][["paramHeader"]] <- 
              lapply(phlist, function(xx) paste0(xx, collapse = "."))

        oldcols <- colnames(outList[["parameters"]][[aname]])
        colnames(outList[["parameters"]][[aname]]) <- ifelse(oldcols %in% names(newheaders), newheaders[oldcols], oldcols)
    }

    res <- list(output = outList,
                mplusKey = mplusKey,
                formula = formula,
                mplusFile = paste0(mplusDir, "mplus.out"))
    class(res) <- "stages"
    invisible(res)
}


summary.stages <- function(object = NULL, type = "unstandardized", trimrows = TRUE, ...)
{
    ## Check for type as character
    if(is.character(type)){
    type <- match.arg(tolower(type), 
                                c('unstandardized', 'std.standardized',
                                  'stdy.standardized', 'stdyx.standardized'))
    } else {
    stop(paste("type must equal unstandardized,",
                   "stdyx.standardized, stdy.standardized,", 
                   "or std.standardized."))
    }
    formula <- object$formula   
    coefs <- object[["output"]][["parameters"]][[type]]

    noise <- grep("Means$|Variances$|.*WITH$", coefs$paramHeader)

    paramHeader <- coefs$paramHeader
    if (trimrows & length(noise) > 0){
        coefs <- coefs[-noise, ]
    }
    ## only if trimrows can we tighten up predictor names
    if (trimrows){
        paramHeader <- substr(coefs$paramHeader, 1, 2)
        paramHeader <- gsub("C", "", paramHeader)
    }
    ## Make rownames
    rownames(coefs) <- paste0(coefs$param, ";", paramHeader)
    
    ## JH 2/4/2015
    ## create Th;1, ...., Th;n
    charVec <- paste0('^', rownames(object$mplusKey)[grep('^C\\d{1,}_', rownames(object$mplusKey))], ';.+')
    newThVec <- paste0('Threshold;', 1:length(charVec))
    ## Final rownames
    rownames(coefs) <- multiGsub(charVec, newThVec, rownames(coefs))
    coefs$param <- NULL
    coefs$paramHeader <- NULL
    coefs <- as.matrix(coefs)

    res <- list(coefficients = coefs, N = object[[1]]$summaries$Observations,
                LL = object[[1]]$summaries$LL ,
                AIC = object[[1]]$summaries$AIC,
                BIC = object[[1]]$summaries$BIC,
                aBIC = object[[1]]$summaries$aBIC,
                AICC = object[[1]]$summaries$AICC, formula = formula)
    class(res) <- "summary.stages"
    attr(res, "trimrows") <- trimrows
    attr(res, "type") <- type
    res
}


print.summary.stages <- function(x,
                                 digits = max(3L, getOption("digits") - 3L),
                                 signif.stars = getOption("show.signif.stars"), ....)
{
    coefs <- x$coefficients
    cat(paste("This is", attr(x, "type") , 
        "output from Mplus, reformatted similar to VGAM", "\n"))
    if (attr(x, "trimrows")) cat(paste("Note: Omitting output rows for WITH,",
        "Variances, Means", "\n"))

    printCoefmat(coefs, digits = digits, signif.stars = signif.stars,
                 na.print = "NA")
    cat(paste("N:" , formatC(x$N, digits = digits), "\n"))
    cat(paste("LL:" , formatC(x$LL, digits = digits), "\n"))
    cat(paste("AIC:" , formatC(x$AIC, digits = digits), "\n"))
    cat(paste("BIC:" , formatC(x$BIC, digits = digits), "\n"))
    cat(paste("aBIC:" , formatC(x$aBIC, digits = digits), "\n"))
    cat(paste("AICC:" , formatC(x$AICC, digits = digits), "\n"))
    invisible(coefs)
}

nobs.stages <- function(object, ...){
    object[[1]]$summaries$Observations
}

logLik.stages <- function(object, ...){
    myll <- object[[1]]$summaries$LL
    attr(myll, "df") <- object[[1]]$summaries$Parameters
    myll
}


coef.summary.stages <- function(object, ...){
    ggg <- object$coefficients
}

coef.stages <- function(object, ...){
    objsum <- summary(object)$coefficients
}

Key elements

Review the output from lm and glm, and output from summary.lm and summary.glm
New class stages should use IDENTICAL names for output elements where possible
Note that R summary methods for regressions have a standard format for tables, and the table is accessed by coef(summary(m1))
Methods using common R names need to be provided:
- nobs
- coef
- coef.summary
- logLik
Needs anova method
This "almost" (99.7%) is compatible with outreg regression table generator
Need next: Roxygen markup to document functions

Advice about designing interfaces

new Rchaeology vignette
tidbits
1. Protect your function's calculations from the user's workspace.
2. Check argument values.
3. Design the function so that it runs with a minimum number of arguments.

Now I emphasize 3, the minimum number of arguments

In the development process, we are often unsure which arguments should be passed around.
Often we end up with 3 or 4 related things, "a1", "b1", "c1", "d1" and function declarations have all four of those things passed along.
If those 4 things really are linked, they are always companions, we should more formally link them together. Can
- Put all 4 things into a list, or
- Create a1 and then add b1 c1 d1 as attributes:
```
attr(a1, "b") <- b1
attr(a1, "c") <- c1
attr(a1, "d") <- d1
```

This eliminates the need to write myFunction(a, b, c, d) to receive 4 arguments, we instead write

myFunction <- function (a){
   b <- attr(a, "b")
   c <- attr(a, "c")
   d <- attr(d, "d")
   [blah blah blah]
}

Creating R Classes (S3): Regression Contexts or Similar

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