Get column names where dat is equal to

Question

I have a data frame (df) with 7 rows and 4 columns (named c1, c2, c3, c4):

c1  c2  c3  c4
Yes No  Yes No    
Yes Yes No  No    
No  Yes No  No    
Yes No  No         


        

Answer 1

An option using data.table

library(data.table)
setDT(df)[, rownum:=1:.N,]
df$Expected_result <- melt(df, "rownum")[, 
                         toString(variable[value=="Yes"]), rownum]$V1