使用 dplyr 将字符串列重新编码为整数

Question

如何创建一个新的整数列 recode为现有列重新编码 y在数据框中 df使用 dplyr方法？

# Generates Random data 
df <- data.frame(x = sample(1:100, 50), 
                 y = sample(LETTERS, 50, replace = TRUE), 
                 stringsAsFactors = FALSE)
# Structure of the data
str(df)
# 'data.frame': 50 obs. of  2 variables:
#   $ x: int  90 4 33 85 30 19 78 77 7 10 ...
# $ y: chr  "N" "B" "P" "W" ...

# Making the character vector as factor variable
df$y <- factor(df$y)

# Structure of the data to llok at the effect of factor creation
str(df)
# 'data.frame': 50 obs. of  2 variables:
#   $ x: int  90 4 33 85 30 19 78 77 7 10 ...
# $ y: Factor w/ 23 levels "A","B","C","E",..: 12 2 14 21 12 22 7 1 6 17 ...

# collecting the levels of the factor variable
labs <- levels(df$y)

# Recode the levels to sequential integers
recode <- 1:length(labs)

# Creates the recode dataframe
dfrecode <- data.frame(labs, recode)

# Mapping the recodes to the original data
df$recode <- dfrecode[match(df$y, dfrecode$labs), 'recode']

此代码按预期工作。但我想用 dplyr 或其他有效方法替换这种方法。我可以使用 this approach 实现相同的效果如果我知道所有的值。但我想在不查看或明确列出列中存在的值的情况下执行此操作

Answer 1

这里的诀窍是做 as.numeric(factor)实际上以整数形式返回级别。所以，试试这个

df <- data.frame(x = sample(1:100, 50), 
                 y = sample(LETTERS, 50, replace = TRUE), 
                 stringsAsFactors = FALSE)
library(dplyr)
dfrecode <- df %>%
        mutate(recode = as.numeric(factor(y)))
str(dfrecode)