Creating an “other” field

Question

Right now, I have the following data.frame which was created by original.df %.% group_by(Category) %.% tally() %.% arrange(desc(n)).

DF <- st         


        

Answer 1

This is another approach, assuming that each category (of the top 5 at least) only occurs once:

df %.% 
  arrange(desc(n)) %.%       #you could skip this step since you arranged the input df already according to your question
  mutate(Category = ifelse(1:n() > 5, "Other", Category)) %.%
  group_by(Category) %.%
  summarize(n = sum(n))

#  Category      n
#1        E 163051
#2        I  49701
#3        K 127133
#4        L  64868
#5        M 106680
#6    Other 217022

Edit:

I just noticed that my output is not order by decreasing n any more. After running the code again, I found out that the order is kept until after the group_by(Category) but when I run the summarize afterwards, the order is gone (or rather, it seems to be ordered by Category). Is that supposed to be like that?

Here are three more ways:

m <- 5    #number of top results to show in final table (excl. "Other")
n <- m+1

#preserves the order (or better: reesatblishes it by index)
df <- arrange(df, desc(n)) %.%    #this could be skipped if data already ordered 
  mutate(idx = 1:n(), Category = ifelse(idx > m, "Other", Category)) %.%
  group_by(Category) %.%
  summarize(n = sum(n), idx = first(idx)) %.%
  arrange(idx) %.%
  select(-idx)

#doesnt preserve the order (same result as in first dplyr solution, ordered by Category)
df[order(df$n, decreasing=T),]     #this could be skipped if data already ordered 
df[n:nrow(df),1] <- "Other"
df <- aggregate(n ~ Category, data = df, FUN = "sum")

#preserves the order (without extra index)
df[order(df$n, decreasing=T),]     #this could be skipped if data already ordered 
df[n:nrow(df),1] <- "Other"
df[n,2] <- sum(df$n[df$Category == "Other"]) 
df <- df[1:n,]