在 ifelse R 中 paste0

Question

I try to use paste0 in an ifelse() to create a conditioned new variable in a data table. The code I use is the following:

data[, paste0("inc_2014_",i) := ifelse(paste0("testvar",i) == 2014, 1, 0)]

This does not work. There is no error message but the values of inc_2014_i (in my test case inc_2014_1) are all 0 whereas ther should be a couple of hundreds 1.

If I test

data[, paste0("inc_2014_",i) := ifelse(testvar1 == 2014, 1, 0)]

it works fine.

If I test

paste0("testvar",i)

I get the correct variable as output.

What am I doing wrong?

Answer 1

You need to iterate through your columns to define i, maybe you can try:

for(i in 1:length(grep("inc_2014_", colnames(data))))
{
    data[, paste0("inc_2014_",i) := ifelse(paste0("testvar",i) == 2014, 1, 0)]
}

Answer 2

It's not working, because you are trying to call the variable in the ifelse as a string.

Assuming i = 1, the result of paste0("testvar",i) is "testvar1" but ifelse needs testvar1 , not as a string.

Use the function get() as follows and it should work.

data[, paste0("inc_2014_",i) := ifelse(get(paste0("testvar",i)) == 2014, 1, 0)]