Remove all rows that have a value in `col_b` that does not show-up in `col_a` (question sent)

filter-for-network.R

library(tidyverse, quietly = TRUE)

(df <- tibble(col_a = c("a", "b", "c", "d", "d"),
       col_b = c("b", "a", "d", "a", "e")))
#> # A tibble: 5 x 2
#>   col_a col_b
#>   <chr> <chr>
#> 1 a     b    
#> 2 b     a    
#> 3 c     d    
#> 4 d     a    
#> 5 d     e

filter(df, col_b %in% col_a)
#> # A tibble: 4 x 2
#>   col_a col_b
#>   <chr> <chr>
#> 1 a     b    
#> 2 b     a    
#> 3 c     d    
#> 4 d     a