Rename one named column in R

There is a function setnames built into package data.table for exactly that.

setnames(DT, "b", "d") 

It changes the names by reference with no copy at all. Any other method using names(data)<- or names(data)[i]<- or similar will copy the entire object, usually several times. Even though all you're doing is changing a column name.

DT must be type data.table for setnames to work, though. So you'd need to switch to data.table or convert using as.data.table, to use it.

Here is the extract from ?setnames. The intention is that you run example(setnames) at the prompt and then the comments relate to the copies you see being reported by tracemem.

DF = data.frame(a=1:2,b=3:4) # base data.frame to demo copies tracemem(DF) colnames(DF)[1] <- "A" # 4 copies of entire object names(DF)[1] <- "A" # 3 copies of entire object names(DF) <- c("A", "b") # 2 copies of entire object `names<-`(DF,c("A","b")) # 1 copy of entire object x=`names<-`(DF,c("A","b")) # still 1 copy (so not print method) # What if DF is large, say 10GB in RAM. Copy 10GB just to change a column name? DT = data.table(a=1:2,b=3:4,c=5:6) tracemem(DT) setnames(DT,"b","B") # by name; no match() needed. No copy. setnames(DT,3,"C") # by position. No copy. setnames(DT,2:3,c("D","E")) # multiple. No copy. setnames(DT,c("a","E"),c("A","F")) # multiple by name. No copy. setnames(DT,c("X","Y","Z")) # replace all. No copy. 

This seems like a hack, but the first thing that came to mind was to use grepl() with a sufficiently detailed enough search string to only get the column you want. I'm sure there are better options:

dat <- data.frame(a = 1:3, b = 1:3, c = 1:3) colnames(dat)[grepl("b", colnames(dat))] <- "foo" dat #------ a foo c 1 1 1 1 2 2 2 2 3 3 3 3 

As Joran points out below, I overcomplicated things...no need for a regex at all. This saves a few characters on the typing too.

colnames(dat)[colnames(dat) == "foo"] <- "bar" #------ a bar c 1 1 1 1 2 2 2 2 3 3 3 3 

Yes but it's more difficult (as far as I know) than numeric indexing. I'm going to provide a dirty function that will do this and if you want to see how to do it just tear the function apart line by line:

rename <- function(df, column, new){ x <- names(df) #Did this to avoid typing twice if (is.numeric(column)) column <- x[column] #Take numeric input by indexing names(df)[x %in% column] <- new #What you're interested in return(df) } #try it out rename(mtcars, 'mpg', 'NEW') rename(mtcars, 1, 'NEW') 

I disagree with @Chase - the grepl solution ain't the luckiest one. I'd say: go with simple ==. Here's why:

d <- data.frame(matrix(rnorm(100), 10)) colnames(d) <- replicate(10, paste(sample(letters[1:5], size = 5, replace=TRUE, prob=c(.1, .6, .1, .1, .1)), collapse = "")) 

Now try doing grepl("b", colnames(d)). Either pass fixed = TRUE, or even better do simple colnames(d) == "b" like @joran suggested. Regex matching will always be slower than ==, so for simple tasks like this you may want to use simple ==.