concatenating column names in a loop

Hi all,

I am trying to concatenate words together to create new column names, using a
loop.

Please consider the following toy example:

x <- matrix(nrow = 1, ncol = 3)
colnames(x) <- c("a", "b", "c")
x[1,1] <- "1"
x[1,2] <- "2"
x[1,3] <- "3"

I would like to create a new matrix with column names based on the column names
in x. Specifically, I would like the column names in y to be "q_" plus the
corresponding column name in x. So y[,1] should be named "q_a", y[,2] should be
names "q_b", and y[,3] should be named "q_c".


Here is the code I am trying:

y <- matrix(nrow = nrow(x), ncol = ncol(x))
for (i in 1:ncol(x)){
? ?colnames(y)[i] <- paste("q_", (colnames(x)[i]), sep = "")
}

Alas, it does not work. I get the following error (from the console window):

Error in dimnames(x) <- dn :
?length of 'dimnames' [2] not equal to array extent


Can any of you help to debug my code? Please consider the following constraints:
(1) In reality, my dataset has many more than three columns, so I must use a
loop.
(2) I would like my code to be robust against changes in the column numbers of
the x matrix. That is why I am telling R to look up the number of rows and
columns in the x matrix when constructing the y matrix, rather than just putting
in a hard count for the number of rows and columns in the y matrix.


Thanks in advance,
Josh Banta




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