为 R 中的变量生成标签

Question

我正在寻找一种比这个更好/更快的方法来为变量生成标签：

df <- data.frame(a=c(0,7,1,10,2,4,3,5,10,1,7,8,3,2))
pick <- c(0,1,2,3,10)
df[sapply(df$a,function(x) !(x %in% pick)),"a"] <- "a"
df[sapply(df$a,function(x) x==0),"a"] <- "b"
df[sapply(df$a,function(x) x==1 | x==2 | x==3),"a"] <- "c"
df[sapply(df$a,function(x) x==10),"a"] <- "d"

df$a
[1] "b" "a" "c" "d" "c" "a" "c" "a" "d" "c" "a" "a" "c" "c" 

为了简单起见，我在这个例子中只有一个变量，当然我的数据集中还有更多变量，但我只想更改一个特定的变量。

Answer 1

你不需要sapply:

df$a[!df$a %in% pick] <- "a"
df$a[df$a==0] <- "b"
df$a[df$a %in% 1:3] <- "c"
df$a[df$a==10] <- "d"

您也可以使用因子产生相同的结果：

df <- data.frame(a=c(0,7,1,10,2,4,3,5,10,1,7,8,3,2))

# the above method
a <- df$a
a[!df$a %in% pick] <- "a"
a[df$a==0] <- "b"
a[df$a %in% 1:3] <- "c"
a[df$a==10] <- "d"

# one way that gives a warning
b1 <- factor(df$a, levels=0:10, labels=c("b",rep("c",3),rep("a",6),"d"))

# another way that won't give a warning
b2 <- factor(df$a)
levels(b2) <- c("b",rep("c",3),rep("a",4),"d")
b2 <- as.character(b2)

# a third strategy using `library(car)`
b3 <- car::recode(df$a,"0='b';1:3='c';10='d';else='a'")

# check that all strategies are the same
all.equal(a,as.character(b1))
# [1] TRUE
all.equal(as.character(b1),as.character(b2))
# [1] TRUE
all.equal(as.character(b1),as.character(b3))
# [1] TRUE

Answer 2

您还可以考虑plyr 中的mapvalues 或revalue，尤其是在您处理更多标签时：

df$a <- mapvalues(df$a, c(0, 1, 2, 3, 10), c("b", "c", "c", "c", "d"))
df$a[! df$a %in% c("b", "c", "d")] <- "a" # The !pick values

Answer 3

这是另一个相当简单的解决方案：

names(pick) <- c("b", "c", "c", "c", "d")
x <- names(pick[match(df$a, pick)])
x[is.na(x)] <- "a"
x
# [1] "b" "a" "c" "d" "c" "a" "c" "a" "d" "c" "a" "a" "c" "c"

如果您在“pick”对象中包含NA，那就更简单了。

pick <- c(NA, 0, 1, 2, 3, 10)
names(pick) <- c("a", "b", "c", "c", "c", "d")
names(pick[match(df$a, pick, nomatch = 1)])
# [1] "b" "a" "c" "d" "c" "a" "c" "a" "d" "c" "a" "a" "c" "c"

如果您使用第二种选择，请注意nomatch 采用您要再次匹配的位置的整数值。在这里，nomatch 映射到“NA”，它位于“pick”向量中的第一个位置。如果“NA”在最后一个位置，您可以将其输入为nomatch = 6。

Answer 4

您也可以使用ifelse 函数。

with(df,ifelse(a==0,"b",ifelse(a %in% c(1,2,3),"c",ifelse(a==10,"d","a"))))
 [1] "b" "a" "c" "d" "c" "a" "c" "a" "d" "c" "a" "a" "c" "c"