Using ifelse Within apply

Question

I am trying to make a new column in my dataset give a single output for each and every row, depending on the inputs from pre-existing columns.

In this output column, I d

Answer 1

Let n = length(x). ifelse will return rep(NA, n) if TRUE otherwise rep(length(unique(x)), n). Therefore apply will output a matrix. data$output <- apply(... tries assign a matrix (your result) into a column in your data.frame, data$output. This is the cause of your error.

Your code will run if you just assign your output to a variable instead

out <- apply(data, 1, function(x) {ifelse(x == 0, NA, length(unique(x)))})

If you are not expecting a class(matrix) as your output, but rather a vector, then there is something wrong with the logic of your function.