CODEWITHSUNDEEP
rlist
jack kelly
jack kelly

Reputation: 330

Group a list of elements into nested list based on pattern

I have a list, List_A, which contains elements with a similar pattern. I am trying to nest the similar items based on the pattern. Example below

List_A <- list("Q_2020", "Q_2021", "C_2019", "C_2020", "K_2020")

Output:

# List of 5
# $ : chr "Q_2020"
# $ : chr "Q_2021"
# $ : chr "C_2019"
# $ : chr "C_2020"
# $ : chr "K_2020"

Desired Output:

# List of 3
# $ Q:List of 2
#  ..$ : chr "Q_2020"
#  ..$ : chr "Q_2021"
# $ C:List of 2
# ..$ : chr "C_2019"
# ..$ : chr "C_2020"
# $ K: chr "K_2020"

I know the pattern would be before "_" so I am using sub() to get the pattern - but I would like some input on how I can create the nested lists. My attempt is a bit too noisy: 1) extract pattern i.e. Q, K, C, 2) create nested list skeleton, 3) Loop an if statement.

Any input is appreciated.

Upvotes: 1

Views: 356

Answers (2)

ThomasIsCoding
ThomasIsCoding

Reputation: 102890

Do you need this?

> str(split(List_A, factor(u <- substr(unlist(List_A), 1, 1), levels = unique(u))))
List of 3
 $ Q:List of 2
  ..$ : chr "Q_2020"
  ..$ : chr "Q_2021"
 $ C:List of 2
  ..$ : chr "C_2019"
  ..$ : chr "C_2020"
 $ K:List of 1
  ..$ : chr "K_2020"

Upvotes: 1

akrun
akrun

Reputation: 887951

We could split by substring

v1 <- unlist(List_A)
subv1 <- trimws(v1, whitespace = "_.*")
List_A_new <- lapply(split(v1, factor(subv1, levels = unique(subv1))), as.list)

-output structure

str(List_A_new)
List of 3
 $ Q:List of 2
  ..$ : chr "Q_2020"
  ..$ : chr "Q_2021"
 $ C:List of 2
  ..$ : chr "C_2019"
  ..$ : chr "C_2020"
 $ K:List of 1
  ..$ : chr "K_2020"

Upvotes: 1

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