使用 data.table 和自定义函数从字符串变量中提取变量答案

【问题标题】：extract variable from string variable using data.table and self-defined function使用 data.table 和自定义函数从字符串变量中提取变量
【发布时间】：2020-11-14 10:10:37
【问题描述】：

# simulate data
id=c(1:30)
house_type=sample(c("3STR","2STR","1STR","DETC,1STR","2STR,DETC","OTHERS"),20, replace=TRUE)
house=data.table(id,house_type)

# I want to create a house_type2 variable in house data.table
# In the real data, there are many other house type, with 1/2/3STR embeded in these house_typ. 
# I want to extract the STR (how many story) information from the data.

house[,story:="others"][str_detect("3STR",house_type),story:="3STR"][
  str_detect("2STR",house_type),story:="2STR"][
    str_detect("1STR",house_type),story:="1STR"]

模拟数据看起来很样本；在实际数据中，house_type 字符串有更多的变化。我设法用 data.table 链接语法做到了。但我要求一种更优雅的方式来做到这一点：定义一个函数来提取故事并在 house_type 列上应用函数。

【问题讨论】：

标签： r string data.table

【解决方案1】：

您可以使用正则表达式来提取数字：

library(data.table)
library(stringr)
# simulate data
set.seed(123L)
id=c(1:30)
house_type=sample(c("3STR","2STR","1STR","DETC,1STR","2STR,DETC","OTHERS"),20, replace=TRUE)
house=data.table(id,house_type)
#> Warning in as.data.table.list(x, keep.rownames = keep.rownames, check.names
#> = check.names, : Item 2 has 20 rows but longest item has 30; recycled with
#> remainder.

#OP
house[,story:="others"][str_detect("3STR",house_type),story:="3STR"][
    str_detect("2STR",house_type),story:="2STR"][
        str_detect("1STR",house_type),story:="1STR"]

## Solutions
house[, story2 := as.integer(sub("\\D*(\\d+).*", "\\1", house_type))]
#> Warning in eval(jsub, SDenv, parent.frame()): NAs introduced by coercion
house[, story3 := fifelse(is.na(story2), "other", paste0(story2, "STR"))]

house
#>        id house_type  story story2 story3
#>     <int>     <char> <char>  <int> <char>
#>  1:     1       1STR   1STR      1   1STR
#>  2:     2     OTHERS others     NA  other
#>  3:     3       1STR   1STR      1   1STR
#>  4:     4       2STR   2STR      2   2STR
#>  5:     5       2STR   2STR      2   2STR
#>  6:     6     OTHERS others     NA  other
#>  7:     7       1STR   1STR      1   1STR
#>  8:     8  2STR,DETC others      2   2STR
#>  9:     9  DETC,1STR others      1   1STR
#> 10:    10     OTHERS others     NA  other
#> 11:    11     OTHERS others     NA  other
#> 12:    12       3STR   3STR      3   3STR
#> 13:    13       2STR   2STR      2   2STR
#> 14:    14       1STR   1STR      1   1STR
#> 15:    15  2STR,DETC others      2   2STR
#> 16:    16       1STR   1STR      1   1STR
#> 17:    17       1STR   1STR      1   1STR
#> 18:    18       3STR   3STR      3   3STR
#> 19:    19  DETC,1STR others      1   1STR
#> 20:    20       3STR   3STR      3   3STR
#> 21:    21       1STR   1STR      1   1STR
#> 22:    22     OTHERS others     NA  other
#> 23:    23       1STR   1STR      1   1STR
#> 24:    24       2STR   2STR      2   2STR
#> 25:    25       2STR   2STR      2   2STR
#> 26:    26     OTHERS others     NA  other
#> 27:    27       1STR   1STR      1   1STR
#> 28:    28  2STR,DETC others      2   2STR
#> 29:    29  DETC,1STR others      1   1STR
#> 30:    30     OTHERS others     NA  other
#>        id house_type  story story2 story3

【讨论】：