---
title: "Data Table Guide"
author:
 - name: Paul Johnson
   affiliation: Center for Research Methods and Data Analysis, University of Kansas
   email: pauljohn@ku.edu

date: "`r format(Sys.time(), '%Y %B %d')`" 
output:
   html_document: 
   theme: united 
   highlight: haddock 
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo=TRUE, comment=NA)
options(width = 70)
```

```{r make_pb_dt}
set.seed(234234)
library(data.table)
poolballs <- data.table(
    number = 1:15,
    weight = rnorm(15, 45.7, 0.8),
    diameter = c(3, 2.9, 3.1) #shows recyling
) 
poolballs
```

I want the following to show only head in line 2.
```{r}
poolballs[ , weight2:=2 * weight]
head(poolballs)
```

