Filter a list based on number of columns of tables in R

user_13655050 0
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I have a list of data frames like this: enter image description here I want to know how can I keep data frames with 15 columns and remove other data frames in this list in R.

dplyr tidyverse r
3 Answers

For your future questions, please avoid screenshots and share an actual object using the dput() function.

You can use purrr::keep():

library(tidyverse)
f=function(n) matrix(nrow=2, ncol=n) %>% as.data.frame()
x=list(
   df1=f(15),
   df2=f(15),
   df3=f(6),
   df4=f(6),
   df5=f(15)
)
x %>% keep(~ncol(.x)==15)
#> $df1
#>   V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 V13 V14 V15
#> 1 NA NA NA NA NA NA NA NA NA  NA  NA  NA  NA  NA  NA
#> 2 NA NA NA NA NA NA NA NA NA  NA  NA  NA  NA  NA  NA
#> 
#> $df2
#>   V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 V13 V14 V15
#> 1 NA NA NA NA NA NA NA NA NA  NA  NA  NA  NA  NA  NA
#> 2 NA NA NA NA NA NA NA NA NA  NA  NA  NA  NA  NA  NA
#> 
#> $df5
#>   V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 V13 V14 V15
#> 1 NA NA NA NA NA NA NA NA NA  NA  NA  NA  NA  NA  NA
#> 2 NA NA NA NA NA NA NA NA NA  NA  NA  NA  NA  NA  NA

Created on 2021-10-03 by the reprex package (v2.0.0)

The second argument of purrr::keep() (first when piping) is a predicate function that should return a single logical value depending on whether the column should be kept or not.

user_38880000

We may also do this with Filter from base R

Filter(function(x) ncol(x) == 15, out)

Or another option is sapply to get the number of columns and then create a logical vector to subset the list

out[sapply(out, ncol) == 15]
user_37322710

An alternative to ncol is length. length gives the number of columns of a dataframe:

my_list[sapply(my_list, length)==15]
user_133216470
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