Getting first element of the list in each row in a list-column

How can I get rid of the nested lists and only keep the first element of each list in ColumnB?

It should look like this:

In python, I would try it with a lambda function giving me only the first element of the list.

>Solution :

We can use map to loop over the list column and extract the first element

library(dplyr)
library(purrr)
df1 %>%
    mutate(ColumnB = map_dbl(ColumnB, first))

-output

# A tibble: 3 × 2
  ColumnA ColumnB
  <chr>     <dbl>
1 first         1
2 second        4
3 third         7

Or in base R use sapply to loop over the list and extract the first element

df1$ColumnB <- sapply(df1$ColumnB, `[`, 1)

data

df1 <- structure(list(ColumnA = c("first", "second", "third"), ColumnB = list(
    c(1, 2, 3), c(4, 5, 6), c(7, 8, 9))), class = c("tbl_df", 
"tbl", "data.frame"), row.names = c(NA, -3L))