R: how to which columns contains 1 in the same row

Question

I have a data like the following:

df
col1 col2 col3
0     0   1
1     0   0

and I would like to get a result saying in each row which column has the value 1 and return the column name to me. In each row with the columns of consideration, there will only be exactly one "1". There are other values which will be much larger than 1. Without making a new copy of the data with the only three columns, I want to know if there would be efficient ways to extract out the column name.

Try `max.col(df)` or `names(df)[max.col(df)]` if you want the names — David Arenburg, Oct 04 '16 at 17:59
i edited the question and this is not the same thing as finding the largest value in each row — lll, Oct 04 '16 at 18:36

score 0 · Accepted Answer · answered Oct 04 '16 at 18:01

0

apply(df, 1, function(row_tmp){
    which(row_tmp == 1)
})

answered Oct 04 '16 at 18:01

tobiasegli_te

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Thanks for accepting my answer. I realized that you had asked to extract the column names, simply change the part within the function to `names(df)[which(row_tmp == 1)]` to obtain column names. – tobiasegli_te Oct 04 '16 at 19:19

R: how to which columns contains 1 in the same row

1 Answers1