Adding variable name to column in for statement

Question

I have multiple columns in a table called "Gr1","Gr2",...,"Gr10".

I want to convert the class from character to integer. I want to do it in a dynamic way, I'm trying this, but it doesn't work:

for (i in 1:10) {
  Col <- paste0('Students1$Gr',i)
  Col <- as.integer(Col)
                 }

My objective here is to know how to add dynamically the for variable to the name of a column. Something like:

for (i in 1:10) {
  Students1$Gr(i) <- as.integer(Students1$Gr(i))
                }

Any idea is welcome. Thank you very much, Matias

You want to change a table/matrix from character to integer? is it this what you want? your question is not so clear to me. — and-bri
– and-bri, Commented Jan 5, 2018 at 19:52
The best "R" way to do this would be with an *apply. Something like: cols <- names(Students)[grepl("Gr", names(Students))]; Students[, cols] <- lapply(Students[,cols], as.integer) — Mike H.
– Mike H., Commented Jan 5, 2018 at 19:52
@MikeH.sapply might be better than lapply since we are not working with lists here. — phil_t
– phil_t, Commented Jan 5, 2018 at 19:54
@phil_t I believe we are working with lists. data.frames are lists with a few additional properties (see is.list(data.frame(a=1))). We are trying to replace list elements (the numeric vectors) with other elements (character vectors). sapply would work because it'll return a matrix, but then that has to be put back into list elements when you assign it to the data.frame. Also I dislike sapply because it simplifies the result for you. — Mike H.
– Mike H., Commented Jan 5, 2018 at 20:18

user3170906 · Accepted Answer · 2018-01-05 21:10:58Z

1

# Example matrix
xm <- matrix(as.character(1:100), ncol = 10);
colnames(xm) <- paste0('Gr', 1:10);

# Example data frame
xd <- as.data.frame(xm, stringsAsFactors = FALSE);

# For matrices, this works
xm <- apply(X = xm, MARGIN = 2, FUN = as.integer);

# For data frames, this works
for (i in 1:10) {
    xd[ , paste0('Gr', i)] <- as.integer(xd[ , paste0('Gr', i)]);
    }

answered Jan 5, 2018 at 21:10

user3170906

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