compact way to create filtered dataframes cycling through different values (R)

I have a dataframe with a column named CHR which has discrete values from 1 to 18 (1, 2, 3 …)

I want to subset the dataframes for each value of CHR. So far my code (working) looks like this:

CH1<-boxplot %>% filter(CHR == "1")
CH2<-boxplot %>% filter(CHR == "2")
CH3<-boxplot %>% filter(CHR == "3")
               .
               .
               .
CH18<-boxplot %>% filter(CHR == "18")

It does get the job done, but I’m very annoyed whenever my code looks like that. I want to learn one "proper" way so I can apply it to multiple other similar cases.

>Solution :

You have a few options:

1. Write a function, although you will still have many lines, they are condensed lines.

bx_filter <- function(boxplot, chr) {
  boxplot %>% filter(CHR == chr)
}

CH1 <- bx_filter("1")
CH2 <- bx_filter("2")

2. Use split(), where you’ll get a list and each element of the list has the data frames you’re looking for

split(boxplot, boxplot$CHR)

3. A combo of map() and assign(), although it’s generally frowned upon to write to the Global environment in ways similar to this

unique(boxplot$CHR) %>%
  map(function(chr) {
    assign(paste0('CH', chr), boxplot %>% filter(CHR == chr), envir = .GlobalEnv)
  })