[R] concatenating column names in a loop

[Erik Iverson]

Josh B wrote:
> 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))

Does...

colnames(y) <- paste("q_", colnames(x), sep = "")

work?

<snip>

> 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.

Not true! R has many functions like colnames that are vectorized, i.e., 
operate on vectors of arbitrary length, making for-loops unnecessary!