Filter a list of data frames based on the first value in a column

user_11118331 0
Viewed 56

I have some data, example here:

 dat1 <- data.frame(a = c("5","10","15","20"), b = c("0.1","0.2","0.3","0.4"))
 dat2 <- data.frame(a = c("15","20","25","30"), b = c("0.5","0.6","0.7","0.8"))
 datalist <-list (dat1,dat2)

Giving me a format like this

    [[1]]
   a   b
1  5 0.1
2 10 0.2
3 15 0.3
4 20 0.4

   [[2]]
   a   b
1 15 0.5
2 20 0.6
3 25 0.7
4 30 0.8

I want to be able to filter the list of data frames with the condition that the first value of column a should be <= 10. So in this scenario the output would be just the first data frame [[1]], and the second data frame would be ignored entirely.

Desired output

    [[1]]
   a   b
1  5 0.1
2 10 0.2
3 15 0.3
4 20 0.4

Any advice would be greatly appreciated! Thanks

r
3 Answers

You can use sapply to get a vector of logicals indicating whether each element of a list meets a certain condition. This can then be applied to subset the list in the usual way with [. E.g:

datalist[sapply(datalist, function(x){as.numeric(x[[1,"a"]]) <= 10})]

will return only the first element in your example.

(Note the as.numeric is necessary because your numbers are stored as character strings here)

user_164076450

We can also use keep function from purrr. It takes a predicate function .p and apply it on every element of a list and return those elements that predicate function equals to a single TRUE.

lirbary(purrr)

datalist %>%
  keep(~ .x[["a"]][1] %>% as.numeric() <= 10)

[[1]]
   a   b
1  5 0.1
2 10 0.2
3 15 0.3
4 20 0.4
user_143145200

We may use Filter from base R

Filter(\(x) as.numeric(x$a[1]) <= 10, datalist)
[[1]]
   a   b
1  5 0.1
2 10 0.2
3 15 0.3
4 20 0.4
user_37322710
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