R语言 & Stata：如何对字符串变量实现分组求和和分组累加？

最近有个培训班的小伙伴遇到了这样的问题，他想对字符串变量进行分组求和与分组累加，但是他不知道该如何实现，今天我们就来一起看一下。

Stata 的实现

首先我们先生成一份示例数据：

* 生成示例数据
clear
input int group int x str1 y
1 12 "A"
1 2 "B"
1 35 "C"
1 56 "D"
1 34 "E"
1 24 "F"
1 87 "G"
2 1 "a"
2 36 "b"
2 78 "c"
2 34 "d"
2 12 "e"
2 3 "f"
2 0 "g"
end
list, sep(7)

*>     +----------------+
*>     | group    x   y |
*>     |----------------|
*>  1. |     1   12   A |
*>  2. |     1    2   B |
*>  3. |     1   35   C |
*>  4. |     1   56   D |
*>  5. |     1   34   E |
*>  6. |     1   24   F |
*>  7. |     1   87   G |
*>     |----------------|
*>  8. |     2    1   a |
*>  9. |     2   36   b |
*> 10. |     2   78   c |
*> 11. |     2   34   d |
*> 12. |     2   12   e |
*> 13. |     2    3   f |
*> 14. |     2    0   g |
*>     +----------------+

其中 group 变量是分组变量，x 是数值型变量，y 是字符型变量。

对于数值型变量，egen 的 sum() 函数可以实现分组求和的功能：

bysort group: egen xsum = sum(x)
list, sep(7)

*>     +-----------------------+
*>     | group    x   y   xsum |
*>     |-----------------------|
*>  1. |     1   12   A    250 |
*>  2. |     1    2   B    250 |
*>  3. |     1   35   C    250 |
*>  4. |     1   56   D    250 |
*>  5. |     1   34   E    250 |
*>  6. |     1   24   F    250 |
*>  7. |     1   87   G    250 |
*>     |-----------------------|
*>  8. |     2    1   a    164 |
*>  9. |     2   36   b    164 |
*> 10. |     2   78   c    164 |
*> 11. |     2   34   d    164 |
*> 12. |     2   12   e    164 |
*> 13. |     2    3   f    164 |
*> 14. |     2    0   g    164 |
*>     +-----------------------+

gen 的 sum() 函数可以实现分组累加的功能：

bysort group: gen xcumsum = sum(x)
list, sep(7)

*>     +---------------------------------+
*>     | group    x   y   xsum   xcumsum |
*>     |---------------------------------|
*>  1. |     1   12   A    250        12 |
*>  2. |     1    2   B    250        14 |
*>  3. |     1   35   C    250        49 |
*>  4. |     1   56   D    250       105 |
*>  5. |     1   34   E    250       139 |
*>  6. |     1   24   F    250       163 |
*>  7. |     1   87   G    250       250 |
*>     |---------------------------------|
*>  8. |     2    1   a    164         1 |
*>  9. |     2   36   b    164        37 |
*> 10. |     2   78   c    164       115 |
*> 11. |     2   34   d    164       149 |
*> 12. |     2   12   e    164       161 |
*> 13. |     2    3   f    164       164 |
*> 14. |     2    0   g    164       164 |
*>     +---------------------------------+

但是上面两个都不能应用与字符串变量，但是字符串变量的加法在 Stata 中是可行的，例如：

gen yy = y + y
list, sep(7)

*>     +--------------------------------------+
*>     | group    x   y   xsum   xcumsum   yy |
*>     |--------------------------------------|
*>  1. |     1   12   A    250        12   AA |
*>  2. |     1    2   B    250        14   BB |
*>  3. |     1   35   C    250        49   CC |
*>  4. |     1   56   D    250       105   DD |
*>  5. |     1   34   E    250       139   EE |
*>  6. |     1   24   F    250       163   FF |
*>  7. |     1   87   G    250       250   GG |
*>     |--------------------------------------|
*>  8. |     2    1   a    164         1   aa |
*>  9. |     2   36   b    164        37   bb |
*> 10. |     2   78   c    164       115   cc |
*> 11. |     2   34   d    164       149   dd |
*> 12. |     2   12   e    164       161   ee |
*> 13. |     2    3   f    164       164   ff |
*> 14. |     2    0   g    164       164   gg |
*>     +--------------------------------------+

那我们如何在字符串变量上实现分组求和以及分组累加的功能呢？

可以通过设计下面的命令实现：

实现 egen 的 sum() 功能，也就是分组求和：

gen ysum = ""
levelsof group, local(group)
foreach i in `group' {
 di "`i'"
 local `i' = ""
 forval j = 1/`=_N'{
  if `=group[`j']' == `i'{
   local `i' = "``i''`=y[`j']'"
  }
 }
 replace ysum = "``i''" if group == `i'
}
list, sep(7)

*>     +------------------------------------------------+
*>     | group    x   y   xsum   xcumsum   yy      ysum |
*>     |------------------------------------------------|
*>  1. |     1   12   A    250        12   AA   ABCDEFG |
*>  2. |     1    2   B    250        14   BB   ABCDEFG |
*>  3. |     1   35   C    250        49   CC   ABCDEFG |
*>  4. |     1   56   D    250       105   DD   ABCDEFG |
*>  5. |     1   34   E    250       139   EE   ABCDEFG |
*>  6. |     1   24   F    250       163   FF   ABCDEFG |
*>  7. |     1   87   G    250       250   GG   ABCDEFG |
*>     |------------------------------------------------|
*>  8. |     2    1   a    164         1   aa   abcdefg |
*>  9. |     2   36   b    164        37   bb   abcdefg |
*> 10. |     2   78   c    164       115   cc   abcdefg |
*> 11. |     2   34   d    164       149   dd   abcdefg |
*> 12. |     2   12   e    164       161   ee   abcdefg |
*> 13. |     2    3   f    164       164   ff   abcdefg |
*> 14. |     2    0   g    164       164   gg   abcdefg |
*>     +------------------------------------------------+

实现 gen 的 sum() 功能，也就是分组累加：

gen ycumsum = ""
levelsof group, local(group)
foreach i in `group' {
 local `i' = ""
 forval j = 1/`=_N'{
  if `=group[`j']' == `i'{
   local `i' = "``i''`=y[`j']'"
  }
  replace ycumsum = "``i''" if group == `i' & _n == `j'
 }
}
list, sep(7)

*>     +----------------------------------------------------------+
*>     | group    x   y   xsum   xcumsum   yy      ysum   ycumsum |
*>     |----------------------------------------------------------|
*>  1. |     1   12   A    250        12   AA   ABCDEFG         A |
*>  2. |     1    2   B    250        14   BB   ABCDEFG        AB |
*>  3. |     1   35   C    250        49   CC   ABCDEFG       ABC |
*>  4. |     1   56   D    250       105   DD   ABCDEFG      ABCD |
*>  5. |     1   34   E    250       139   EE   ABCDEFG     ABCDE |
*>  6. |     1   24   F    250       163   FF   ABCDEFG    ABCDEF |
*>  7. |     1   87   G    250       250   GG   ABCDEFG   ABCDEFG |
*>     |----------------------------------------------------------|
*>  8. |     2    1   a    164         1   aa   abcdefg         a |
*>  9. |     2   36   b    164        37   bb   abcdefg        ab |
*> 10. |     2   78   c    164       115   cc   abcdefg       abc |
*> 11. |     2   34   d    164       149   dd   abcdefg      abcd |
*> 12. |     2   12   e    164       161   ee   abcdefg     abcde |
*> 13. |     2    3   f    164       164   ff   abcdefg    abcdef |
*> 14. |     2    0   g    164       164   gg   abcdefg   abcdefg |
*>     +----------------------------------------------------------+

这样就完成了！

R 语言的实现

使用 R 语言完成这个工作更容易些，首先我们读取上面生成的示例数据：

library(tidyverse)
haven::read_dta('strsum.dta') -> df
df

#> # A tibble: 14 x 3
#>    group     x y
#>    <dbl> <dbl> <chr>
#>  1     1    12 A
#>  2     1     2 B
#>  3     1    35 C
#>  4     1    56 D
#>  5     1    34 E
#>  6     1    24 F
#>  7     1    87 G
#>  8     2     1 a
#>  9     2    36 b
#> 10     2    78 c
#> 11     2    34 d
#> 12     2    12 e
#> 13     2     3 f
#> 14     2     0 g

x 变量是数值型变量，分组求和或累加都很容易：

df %>%
  group_by(group) %>%
  mutate(xsum = sum(x)) %>%
  mutate(xcumsum = cumsum(x)) %>%
  ungroup()

#> # A tibble: 14 x 5
#>    group     x y      xsum xcumsum
#>    <dbl> <dbl> <chr> <dbl>   <dbl>
#>  1     1    12 A       250      12
#>  2     1     2 B       250      14
#>  3     1    35 C       250      49
#>  4     1    56 D       250     105
#>  5     1    34 E       250     139
#>  6     1    24 F       250     163
#>  7     1    87 G       250     250
#>  8     2     1 a       164       1
#>  9     2    36 b       164      37
#> 10     2    78 c       164     115
#> 11     2    34 d       164     149
#> 12     2    12 e       164     161
#> 13     2     3 f       164     164
#> 14     2     0 g       164     164

那么对于字符串变量 y 该如何分组求和（连接）或者累加（逐次连接）呢？

根据我的经验，分组求和很简单：

df %>%
  group_by(group) %>%
  mutate(ysum = paste0(y, collapse = ""))

#> # A tibble: 14 x 4
#> # Groups:   group [2]
#>    group     x y     ysum
#>    <dbl> <dbl> <chr> <chr>
#>  1     1    12 A     ABCDEFG
#>  2     1     2 B     ABCDEFG
#>  3     1    35 C     ABCDEFG
#>  4     1    56 D     ABCDEFG
#>  5     1    34 E     ABCDEFG
#>  6     1    24 F     ABCDEFG
#>  7     1    87 G     ABCDEFG
#>  8     2     1 a     abcdefg
#>  9     2    36 b     abcdefg
#> 10     2    78 c     abcdefg
#> 11     2    34 d     abcdefg
#> 12     2    12 e     abcdefg
#> 13     2     3 f     abcdefg
#> 14     2     0 g     abcdefg

分组累加我们先找一个向量试试：

letters
#>  [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r"
#> [19] "s" "t" "u" "v" "w" "x" "y" "z"

letters2 <- c()
for (i in 1:length(letters)) {
  letters2[i] <- paste0(letters[1:i], collapse = "")
}
letters2
#>  [1] "a"                          "ab"
#>  [3] "abc"                        "abcd"
#>  [5] "abcde"                      "abcdef"
#>  [7] "abcdefg"                    "abcdefgh"
#>  [9] "abcdefghi"                  "abcdefghij"
#> [11] "abcdefghijk"                "abcdefghijkl"
#> [13] "abcdefghijklm"              "abcdefghijklmn"
#> [15] "abcdefghijklmno"            "abcdefghijklmnop"
#> [17] "abcdefghijklmnopq"          "abcdefghijklmnopqr"
#> [19] "abcdefghijklmnopqrs"        "abcdefghijklmnopqrst"
#> [21] "abcdefghijklmnopqrstu"      "abcdefghijklmnopqrstuv"
#> [23] "abcdefghijklmnopqrstuvw"    "abcdefghijklmnopqrstuvwx"
#> [25] "abcdefghijklmnopqrstuvwxy"  "abcdefghijklmnopqrstuvwxyz"

这样我们就可以自己编写一个函数：

strcumsum <- function(x){
  c <- c()
  for (i in 1:length(x)) {
    c[i] <- paste0(x[1:i], collapse = "")
  }
  return(c)
}
strcumsum(letters)

然后就可以用这个函数对字符串变量进行分组累加了：

df %>%
  group_by(group) %>%
  mutate(ysum = paste0(y, collapse = "")) %>%
  mutate(ycumsum = strcumsum(y))

#> # A tibble: 14 x 5
#> # Groups:   group [2]
#>    group     x y     ysum    ycumsum
#>    <dbl> <dbl> <chr> <chr>   <chr>
#>  1     1    12 A     ABCDEFG A
#>  2     1     2 B     ABCDEFG AB
#>  3     1    35 C     ABCDEFG ABC
#>  4     1    56 D     ABCDEFG ABCD
#>  5     1    34 E     ABCDEFG ABCDE
#>  6     1    24 F     ABCDEFG ABCDEF
#>  7     1    87 G     ABCDEFG ABCDEFG
#>  8     2     1 a     abcdefg a
#>  9     2    36 b     abcdefg ab
#> 10     2    78 c     abcdefg abc
#> 11     2    34 d     abcdefg abcd
#> 12     2    12 e     abcdefg abcde
#> 13     2     3 f     abcdefg abcdef
#> 14     2     0 g     abcdefg abcdefg

点击这里跳转到 RStata 短书平台获取附件：R语言 & Stata：如何对字符串变量实现分组求和和分组累加？

Stata 的实现

R 语言的实现

相关文章

评论