Find the shortest string by categories R

user_12806025 0
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I am quite a beginner in R, and I faced this problem.

I would like to find the length of the shortest string per each category in my tibble and then, truncate all strings from the category according to width of the shortest one.

  ex = tibble( category = c("A", "A", "C", "B", "C", "A"),
           string = c("cat", "bird", "apple", "cloud", "banana", "elephant"))

I presume how to solve the problem theoretically, however, I am not able to put it together.

ex %>% 
 group_by(category) %>%
 mutate(length = lapply(ex, function(x) min(nchar(x))) ) %>%
 somehow str_trunc() ?

At the end I would like to see something like that:

ex = tibble( category = c("A", "A", "C", "B", "C", "A"),
    string = c("cat", "bir", "apple", "cloud", "banan", "ele"))
tidyverse r
2 Answers

This should do what you need

ex %>% 
  group_by(category) %>%
  mutate(length = min(nchar(string)),
         string = str_sub(string, 1, length))

We don't need the lapply inside the mutate to find the length. We can just run that transformation on the string column directly. And here I used stringr::str_sub to get the substring with the right number of characters since you already seem to be using tidyverse functions. You could also use the base substr function instead.

user_23720640

You can do this in base R with 

aggregate(ex$string, list(ex$category),
    function(s) min(nchar(as.character(s))))
user_47526750
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