r - Find the most frequent value by row

Question

My problem is as follows:

I have a data set containing several factor variables, which have the same categories. I need to find the category, which occurs most frequently for each row. In case of ties an arbitrary value can be chosen, although it would be great if I can have more control over it.

My data set contains over a hundred factors. However, the structure is something like that:

df = data.frame(id = 1:3
                var1 = c("red","yellow","green")
                var2 = c("red","yellow","green")
                var3 = c("yellow","orange","green")
                var4 = c("orange","green","yellow"))

df
#   id   var1   var2   var3   var4
# 1  1    red    red yellow orange
# 2  2 yellow yellow orange  green
# 3  3  green  green  green yellow

The solution should be a variable within the data frame, for example var5, which contains the most frequent category for each row. It can be a factor or a numeric vector (in case the data need to be converted first to numeric vectors)

In this case, I would like to have this solution:

df$var5
# [1] "red"    "yellow" "green" 

Any advice will be much appreciated! Thanks in advance!

Answer 1

Something like :

apply(df,1,function(x) names(which.max(table(x))))
[1] "red"    "yellow" "green" 

In case there is a tie, which.max takes the first max value. From the which.max help page :

Determines the location, i.e., index of the (first) minimum or maximum of a numeric vector.

Ex :

var4 <- c("yellow","green","yellow")
df <- data.frame(cbind(id, var1, var2, var3, var4))

> df
  id   var1   var2   var3   var4
1  1    red    red yellow yellow
2  2 yellow yellow orange  green
3  3  green  green  green yellow

apply(df,1,function(x) names(which.max(table(x))))
[1] "red"    "yellow" "green"