Removing a specific number from all lists in a column of lists in R

Question

I have a column in a dataframe that stores lists. Here is an example below:

           col
1   9, 8, 3, 7
2   8, 8, 8, 5
3   1, 8, 10, 4
4   3, 6, 1, 6
5   9, 9, 10, 4
6   8, 8, 9, 2
7   6, 10, 4, 7
8   6, 1, 5, 9
9   4, 7, 5, 10
10  7, 9, 2, 5

This is the code I used to generate the above example:

example <- data.frame(matrix(NA_real_, nrow=10, ncol=1))
colnames(example) <- "col"
x <- list(c(1,2,3,4))
for(y in 1:10) {
  example$col[y] <- list(c(c(sample(1:10,1)),c(sample(1:10,1)),c(sample(1:10,1)),c(sample(1:10,1))))
}

I want to remove all occurrences of the number 9 from all of these lists, in this column of my data frame, to get something like this:

           col
1   8, 3, 7
2   8, 8, 8, 5
3   1, 8, 10, 4
4   3, 6, 1, 6
5   10, 4
6   8, 8, 2
7   6, 10, 4, 7
8   6, 1, 5
9   4, 7, 5, 10
10  7, 2, 5

I'm currently trying to do something like this to go about this problem:

lapply(example, `[<-`, , "col", function(x) ifelse(x==1, NULL, 1))

I keep getting the following error:

Error in lapply(example, `[<-`, , "col", function(x) ifelse(x == 1, NULL,  : 
  incorrect number of subscripts on matrix

How can I resolve this error and fix my problem? Are there any other ways to solve this?

Answer 1

data

set.seed(123) # make sure to set.seed with random draws
example <- data.frame(matrix(NA_real_, nrow=10, ncol=1))
colnames(example) <- "col"
x <- list(c(1,2,3,4))
for(y in 1:10) {
  example$col[y] <- list(c(c(sample(1:10,1)),c(sample(1:10,1)),c(sample(1:10,1)),c(sample(1:10,1))))
}

example
            col
1    3, 8, 5, 9
2   10, 1, 6, 9
3   6, 5, 10, 5
4    7, 6, 2, 9
5   3, 1, 4, 10
6   9, 7, 7, 10
7    7, 8, 6, 6
8  3, 2, 10, 10
9    7, 8, 1, 5
10   8, 3, 4, 3

solution:

library(purrr)
example$col <- map(example$col, ~.x[.x != 9])
example

            col
1       3, 8, 5
2      10, 1, 6
3   6, 5, 10, 5
4       7, 6, 2
5   3, 1, 4, 10
6      7, 7, 10
7    7, 8, 6, 6
8  3, 2, 10, 10
9    7, 8, 1, 5
10   8, 3, 4, 3

Answer 2

Here is the way I would solve it using the purrr package. The map function is similar to lapply (you may need to install the tidyverse package if you haven't already):

library(tidyverse)
example %>% 
  mutate(col = map(col, ~gsub("9", NA_real_, .x)))

result:

            col
1   6, 10, 8, 8
2    3, 7, 1, 1
3    1, 2, 2, 4
4    2, 4, 6, 1
5   10, 8, 2, 8
6  NA, NA, 2, 4
7   5, 7, 8, NA
8  NA, 7, 6, 10
9   2, 6, 4, NA
10 4, 2, 10, 10

Answer 3

Base R:

> example
           col
1  10, 9, 3, 9
2   4, 7, 9, 3
3   5, 9, 5, 3
4   5, 4, 5, 4
5  10, 6, 2, 6
6   4, 7, 5, 9
7   1, 7, 1, 6
8  4, 9, 2, 10
9   3, 9, 3, 2
10  1, 6, 1, 4

example$col <- lapply(example$col, function(x){
  x[x != 9]
})

> example
           col
1        10, 3
2      4, 7, 3
3      5, 5, 3
4   5, 4, 5, 4
5  10, 6, 2, 6
6      4, 7, 5
7   1, 7, 1, 6
8     4, 2, 10
9      3, 3, 2
10  1, 6, 1, 4