Question

In R, assume there is a data frame “mydata” comprising the independent variable “group” (two groups) and n dependent variables. I want to run n t-tests (one for each dependent variable), print and save the results in a file by doing the following:

variables<-names(mydata)
variables<-variables[-1] #to remove the group variable
capture.output(for(i in variables){print(t.test(get(paste("mydata$", i, sep=""))~mydata$group))},file="outputfile.txt")

This command returns the following error message:

Error in get(paste("mydata$", i, sep = "")) : object 'mydata$variable1' not found

What am I doing wrong?

Answer 1

For others, some sample data:

mydata <- data.frame(group=sample(1:2, 100, replace=T), variable1=rnorm(100), variable2=rnorm(100), variable3=rnorm(100))

I’d use the much more straight forward:

for(i in variables) {
   t.test(mydata[i], mydata$group)
}

if I were using a for loop. However, you could do this using a more R-like style:

lapply(variables, function(v, df=mydata) t.test(df[v], df$group))