根据R中的条件重命名因子级别 [英] Rename factor levels based on a condition in R

问题描述

我想将所有小于n的因子合并为一个名为"Else"的因子

I want to combine all factors with a count less than n into one factor named "Else"

例如，如果n = 3，则在以下df中，我想将"c"，"d"和"e"组合为"Else":

For example if n = 3 then in the following df I want to combine "c", "d" and "e" as "Else":

df = data.frame(x=c(1:10), y=c("a","a","a","b","b","b","c","d","d","e"))

我首先获得了具有所有低计数值的df:

I started out by getting a df with all the low count values:

library(plyr)
lowcounts = ddply(df, "y", function(z){if(nrow(z)<3) nrow(z) else NULL})

我知道我可以手动更改这些设置，但实际上我有数十个级别，因此需要使其自动化.

I know I could change these manually but in practice I have dozens of levels so I need to automate this.

我只想选择并重命名level(df)中％low％低级别的级别，其余的保持不变，但不确定如何进行.

I want to select and rename only the levels %in% lowcount in levels(df) and leave the rest the same but not sure how to proceed.

推荐答案

另一种选择:

#your dataframe
df = data.frame(x=c(1:10), y=c("a","a","a","b","b","b","c","d","d","e"))

#which levels to keep and which to change
res <- table(df$y)
notkeep <- names(res[res < 3])
keep <- names(res)[!names(res) %in% notkeep]
names(keep) <- keep

#set new levels
levels(df$y) <- c(keep, list("else" = notkeep))

df
#    x    y
#1   1    a
#2   2    a
#3   3    a
#4   4    b
#5   5    b
#6   6    b
#7   7 else
#8   8 else
#9   9 else
#10 10 else

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