Question

我想将所有因子少于n的因子组合成一个名为＆＃34; Else＆＃34;

的因子

例如，如果n = 3，那么在下面的df中，我想要结合＆＃34; c＆＃34;，＆＃34; d＆＃34;和＆＃34; e＆＃34; as＆＃34; Else＆＃34;：

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

我开始时得到一个包含所有低计数值的df：

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，但在实践中我有几十个级别，所以我需要自动化这个。

我想在级别（df）中选择并重命名％lowcount中的级别％，并将其余部分保持不变但不确定如何继续。

Answer 1

为什么不是这样的？

library(data.table)
dt <- data.table(df)
dt[,ynew := ifelse(.N < 3, "else",as.character(y)), by = "y"]

Answer 2

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

根据R中的条件重命名因子级别

2 个答案: