I have a DF where I want to add a new variable called "B" into the 2nd position.
A C D
1 1 5 2
2 3 3 7
3 6 2 3
4 6 4 8
5 1 1 2
Anyone have an idea?
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The easiest way would be to add the columns you want and then reorder them:
dat$B <- 1:5
newdat <- dat[, c("A", "B", "C", "D")]
Another way:
newdat <- cbind(dat[1], B=1:5, dat[,2:3])
If you're concerned about overhead, perhaps a data.table solution? (With help from this answer):
library(data.table)
dattable <- data.table(dat)
dattable[,B:=1:5]
setcolorder(dattable, c("A", "B", "C", "D"))
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sebastian-c
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1this would work but with an immense overhead if the dataframe has hundreds of variables – Diegoal Feb 12 '13 at 12:21
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Yea exactly my data frame is huge and I want to do this. Also my data frame might change from time to time so I don't want to reference a specific numbered position – Alejandro Ochoa Oct 18 '16 at 15:31
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If you don't want a specific numbered position, how do you know where to put it? – sebastian-c Oct 20 '16 at 16:33
1
dat$B <- 1:5
ind <- c(1:which(names(data) == "A"),ncol(data),(which(names(data) == "A")+1):ncol(data)-1)
data <- data[,ind]
Create the variable at the end of the data.frame and then using an indicator vector signaling how to reorder the columns. ind is just a vector of numbers
Alejandro Ochoa
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Thank you for your answer! I have (and most of us do have) a data frame with more than only a few variables, so putting in every column name or number manually would be too much effort! However, your code should be adjusted as follows: `(ncol(data)-1)`. If you forget the extra brackets, column A gets a copy A.1. – Poza Mar 22 '21 at 16:04