Clash Royale CLAN TAG

R: How to retrieve a column name of a data frame

I am trying to extract the colnames of a data frame, based on the values in the cells. My data is a series of a couple hundred categories, with a simple binary 0 or 1 in the cells to indicate which column name I want in my new df.

To illustrate my point:

year cat1 cat2 cat3 ... catN
2000 0 0 1 0
2001 1 0 0 0
2002 0 0 0 1
....
2018 0 1 0 0


I am trying to get a df like:

year category
2000 cat3
2001 cat1
2002 catN
....
2018 cat2


My code:

newdf <- as.data.frame(colnames(mydf)[which(mydf == "1", arr.ind = TRUE)[2]])


But alas this only returns one category name!

Any help would be greatly appreciated!

1 Answer
1

A possible solution is this:

library(tidyverse)

df = data.frame(year = 2000:2002,
cat1 = c(0,0,1),
cat2 = c(1,0,0),
cat3 = c(0,1,0))

df %>%
gather(category, value, -year) %>% # reshape data
filter(value == 1) %>% # keep rows with 1s
select(-value) %>% # remove that column
arrange(year) # order that column (if needed)

# year category
# 1 2000 cat2
# 2 2001 cat3
# 3 2002 cat1


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