Chirayu Chamoli - 1 year ago 83
R Question

# Collapsing factor level for all the factor variable in dataframe based on the count

I would like to keep only the top 2 factor levels based on the frequency and group all other factors into Other. I tried this but it doesnt help.

``````df=data.frame(a=as.factor(c(rep('D',3),rep('B',5),rep('C',2))),
b=as.factor(c(rep('A',5),rep('B',5))),
c=as.factor(c(rep('A',3),rep('B',5),rep('C',2))))

myfun=function(x){
if(is.factor(x)){
levels(x)[!levels(x) %in% names(sort(table(x),decreasing = T)[1:2])]='Others'
}
}

df=as.data.frame(lapply(df, myfun))
``````

Expected Output

``````       a b      c
D A      A
D A      A
D A      A
B A      B
B A      B
B B      B
B B      B
B B      B
others B others
others B others
``````

This might get a bit messy, but here is one approach via base R,

``````fun1 <- function(x){levels(x) <-
c(names(sort(table(x), decreasing = TRUE)[1:2]),
rep('others', length(levels(x))-2));
return(x)}
``````

However the above function will need to first be re-ordered and as OP states in comment, the correct one will be,

``````fun1 <- function(x){ x=factor(x,
levels = names(sort(table(x), decreasing = TRUE)));
levels(x) <- c(names(sort(table(x), decreasing = TRUE)[1:2]),
rep('others', length(levels(x))-2));
return(x) }
``````
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