twitterで目に留まったのでメモ。

重複しているデータの個数をカウントするときにdplyrでこういう書き方もできるよという話。

library(tidyverse)

## -- Attaching packages --------------------------------------- tidyverse 1.3.0 --

## √ ggplot2 3.3.3     √ purrr   0.3.4
## √ tibble  3.0.5     √ dplyr   1.0.3
## √ tidyr   1.1.2     √ stringr 1.4.0
## √ readr   1.4.0     √ forcats 0.5.1

## -- Conflicts ------------------------------------------ tidyverse_conflicts() --
## x dplyr::filter() masks stats::filter()
## x dplyr::lag()    masks stats::lag()

view(starwars)

starwars %>% 
  left_join(starwars %>% 
              group_by(homeworld) %>% 
              summarise(n=n()),
            by="homeworld") %>% 
  filter(n>1)

## # A tibble: 48 x 15
##    name  height  mass hair_color skin_color eye_color birth_year sex   gender
##    <chr>  <int> <dbl> <chr>      <chr>      <chr>          <dbl> <chr> <chr> 
##  1 Luke~    172    77 blond      fair       blue            19   male  mascu~
##  2 C-3PO    167    75 <NA>       gold       yellow         112   none  mascu~
##  3 R2-D2     96    32 <NA>       white, bl~ red             33   none  mascu~
##  4 Dart~    202   136 none       white      yellow          41.9 male  mascu~
##  5 Leia~    150    49 brown      light      brown           19   fema~ femin~
##  6 Owen~    178   120 brown, gr~ light      blue            52   male  mascu~
##  7 Beru~    165    75 brown      light      blue            47   fema~ femin~
##  8 R5-D4     97    32 <NA>       white, red red             NA   none  mascu~
##  9 Bigg~    183    84 black      light      brown           24   male  mascu~
## 10 Anak~    188    84 blond      fair       blue            41.9 male  mascu~
## # ... with 38 more rows, and 6 more variables: homeworld <chr>, species <chr>,
## #   films <list>, vehicles <list>, starships <list>, n <int>

starwars %>% 
  group_by(homeworld) %>% 
  filter(n()>1)

## # A tibble: 48 x 14
## # Groups:   homeworld [10]
##    name  height  mass hair_color skin_color eye_color birth_year sex   gender
##    <chr>  <int> <dbl> <chr>      <chr>      <chr>          <dbl> <chr> <chr> 
##  1 Luke~    172    77 blond      fair       blue            19   male  mascu~
##  2 C-3PO    167    75 <NA>       gold       yellow         112   none  mascu~
##  3 R2-D2     96    32 <NA>       white, bl~ red             33   none  mascu~
##  4 Dart~    202   136 none       white      yellow          41.9 male  mascu~
##  5 Leia~    150    49 brown      light      brown           19   fema~ femin~
##  6 Owen~    178   120 brown, gr~ light      blue            52   male  mascu~
##  7 Beru~    165    75 brown      light      blue            47   fema~ femin~
##  8 R5-D4     97    32 <NA>       white, red red             NA   none  mascu~
##  9 Bigg~    183    84 black      light      brown           24   male  mascu~
## 10 Anak~    188    84 blond      fair       blue            41.9 male  mascu~
## # ... with 38 more rows, and 5 more variables: homeworld <chr>, species <chr>,
## #   films <list>, vehicles <list>, starships <list>

上と下とで同じデータが生成される。