\begin{Schunk}
\begin{Sinput}
 mergeCheck(df1, df2, by.x = "idx", by.y = "idy")
\end{Sinput}
\begin{Soutput}
Merge difficulties detected

Unacceptable key values
df1 
  idx           x
6  NA  1.31923172
7 NaN -0.08075376
Unmatched cases from df1 and df2 :
df1 
  idx           x
1   1 -0.44803329
6  NA  1.31923172
7 NaN -0.08075376
df2 
  idy           x
5   6 -0.06901731
6   9  1.54486360
7  10  1.32145202
\end{Soutput}
\end{Schunk}
