ECII ECII - 3 months ago 60
R Question

move column to first in a data frame

I have a data frame which I want to export to csv. For readability issues I would like to have the last column of the data frame moved to the start (as first column). How can I do it in R?

My data.frame has about a thousand columns to changing the order wont to. I just want to pick one column and "move it to the start".

Answer

I don't know if it's worth adding this as an answer or if a comment would be fine, but I wrote a function called moveme that lets you do what you want to do with the language you describe. You can find the function at this answer: http://stackoverflow.com/a/18540144/1270695

It works on the names of your data.frame and produces a character vector that you can use to reorder your columns:

mydf <- data.frame(matrix(1:12, ncol = 4))
mydf
moveme(names(mydf), "X4 first")
# [1] "X4" "X1" "X2" "X3"
moveme(names(mydf), "X4 first; X1 last")
# [1] "X4" "X2" "X3" "X1"

mydf[moveme(names(mydf), "X4 first")]
#   X4 X1 X2 X3
# 1 10  1  4  7
# 2 11  2  5  8
# 3 12  3  6  9

If you're shuffling things around like this, I suggest converting your data.frame to a data.table and using setcolorder (with my moveme function, if you wish) to make the change by reference.


In your question, you also mentioned "I just want to pick one column and move it to the start". If it's an arbitrary column, and not specifically the last one, you could also look at using setdiff.

Imagine you're working with the "mtcars" dataset and want to move the "am" column to the start.

x <- "am"
mtcars[c(x, setdiff(names(mtcars), x))]
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