Test statistic (e.g. chisquare test) inside latex table using the tables-package in R/Knitr/Rstudio

Question

I would like to use the tabular()-function from the tables-package to do a cross-tabulation of two variables (e.g. v1 and v2), and present the p-value of the chisq-test in the table. It is easy to get the crosstabulation, but I cant get the p-value inside the table. This is what I've been trying, without any luck:

\documentclass{article}

\begin{document}

<<echo=TRUE,message=FALSE>>=
library(Hmisc)
library(tables)
v1 <- sample(letters[1:2],200,replace=TRUE)
v2 <- sample(month.name[1:3],200,replace=TRUE)
df <- data.frame(v1,v2)
@

It is straight forward to get the crosstabulation:
<<results='asis'>>=
latex(   tabular(    Factor(v1)   ~   Factor(v2)      , data=df)  )
@

But I cant get the p-value inside the table:

<<results='asis'>>=
latex(   tabular(    Factor(v1)*chisq.test(v1,v2)$p.value   ~   Factor(v2)      , data=df)  )
@

\end{document}

Answer 1

I don't know how to do it with tables::tabular but this will do it with Hmisc::summary.formula.reverse assuming you have your system configured to produce pdf files through latex(). I had to do searching of the Rhelp archives to figure out that the 'exclude1' argument needed to go in the latex argument list. Once you go back through the documentation exclude1 does appear in the usage example of latex.summary.formula.reverse although I thought I was reading the help page for summary.rms:

library(Hmisc)
latex(summary( v2 ~ v1, data=df,  method="reverse" ,test=TRUE), exclude1=FALSE)

You can intercept the latex output "along the way" if you want to embed it in a longer document by assigning the output to a named file.

latex(summary( v2 ~ v1, data=df,  method="reverse" ,test=TRUE), exclude1=FALSE, file="")
#--------
% latex.default(cstats, title = title, caption = caption, rowlabel = rowlabel,      col.just = col.just, numeric.dollar = FALSE, insert.bottom = legend,      rowname = lab, dcolumn = dcolumn, extracolheads = extracolheads,      extracolsize = Nsize, ...) 
%
\begin{table}[!tbp]
\caption{Descriptive Statistics by v2\label{summary}} 
\begin{center}
\begin{tabular}{lcccc}
\hline\hline
\multicolumn{1}{l}{}&\multicolumn{1}{c}{February}&\multicolumn{1}{c}{January}&\multicolumn{1}{c}{March}&\multicolumn{1}{c}{Test Statistic}\tabularnewline
&\multicolumn{1}{c}{{\scriptsize $N=56$}}&\multicolumn{1}{c}{{\scriptsize $N=73$}}&\multicolumn{1}{c}{{\scriptsize $N=71$}}&\tabularnewline
\hline
v1~:~a&43\%~{\scriptsize~(24)}&47\%~{\scriptsize~(34)}&44\%~{\scriptsize~(31)}&$ \chi^{2}_{2}=0.21 ,~ P=0.901  $\tabularnewline
~~~~b&57\%~{\scriptsize~(32)}&53\%~{\scriptsize~(39)}&56\%~{\scriptsize~(40)}&\tabularnewline
\hline
\end{tabular}
\end{center}
Numbers after percents are frequencies.\\\noindent Test used:\\Pearson test\end{table}

Answer 2

You can also paste text from a chi-squared statistic into a caption via xtable(). For example:

#sample data
var1<-sample(c('A', 'B'), 10, replace=T)
var2<-sample(c('Red', 'Blue'), 10, replace=T)
#join in frequency table
tab<-table(var1, var2)
#conduct chisq.test
test<-chisq.test(tab)
#show values of chisq.test()
name(test)
#Use xtable, use print.xtable for further manipulations
out<-xtable(tab, caption=paste('Important table, chi-squared =', test$statistic, ', p=', test$p.value,',' ,test$parameter, 'df', sep=' '))
#print
out