DeltaIV DeltaIV - 16 days ago 4
R Question

How can I gather_ on all columns but one?

I need to

gather_
on all columns of a dataframe, except for one. Example:

# I want to generate a dataframe whose column names are the letters of the alphabet. If you know of a simpler way, let me know!
foo <- as.data.frame(matrix(runif(100), 10, 10))
colnames(foo) <- letters[1:10]


Now, suppose I want to gather on all columns except column
e
. This won't work:

mycol <- "e"
foo_melt <- gather_(foo, key = "variable", value = "value", -mycol)
#Error in -mycol : invalid argument to unary operator


This will:

column_list <- colnames(foo)
column_list <- column_list[column_list != mycol]
foo_melt <- gather_(foo, key = "variable", value = "value", column_list)


Looks quite convoluted if you ask me. Isn't there any simpler way?

Answer

One option is one_of with gather

res1 <- gather(foo, key = "variable", value = "value", -one_of(mycol))

and if we need gather_, then setdiff can be used

res2 <- gather_(foo, key = "variable", value = "value", setdiff(names(foo), mycol))

identical(res1, res2)
#[1] TRUE
dim(res1)
#[1] 90  3

head(res1, 3)
#          e variable     value
#1 0.8484310        a 0.2730847
#2 0.0501665        a 0.8129584
#3 0.6689233        a 0.5457884