Is there an R function for trimming vectors in a list to smallest vector length?

user_17066629 0
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I am trying to write a function that takes a list of vectors, finds the vector with minimum length, and then makes all other vectors in the list that size.

This is what I have so far:

I first create the list of vectors,

data_list <- as.list(vector1, vector2, etc)

Then, I start writing the "trim" function to find vectors that are longer than the vector of smallest length, and reduce their length to the minimum length:

trim <- function(list){
lengths_list <- lengths(list)
min_length <- min(length_numbers)
for(i in list){
if(i > min_length){
list[i] <- list[-1:-min_length]
}
else{
next
}
}
}

When I apply this function to my list of vector, nothing happens. The lengths of the vectors do not change.

What am I doing wrong?

Thanks!

r function
3 Answers

Using @Samet Sökel data (many thanks!), we could do a lapply and find the minimum length of all lists:

lapply(vec_list, function(i)i[seq(min(lengths(vec_list)))])

[[1]]
[1] 1 2 3

[[2]]
[1] 1 2 3

[[3]]
[1] 1 2 3

OR other way:

trim_shortest <- function(x_list) {
n <- min(vapply(x_list, length, min(lengths(vec_list))))
lapply(x_list, head, n)
}

trim_shortest(vec_list)

or as akrun commented:

lapply(vec_list, "[", seq(min(lengths(vec_list))))
user_133216470

without writing a trim function;

a <- 1:3
b <- 1:7
c <- 1:15

vec_list <- list(a,b,c)

min_length <- min(sapply(vec_list,length))

new_list <- lapply(vec_list,function(x) x[1:min_length])
                   
new_list

output;

[[1]]
[1] 1 2 3

[[2]]
[1] 1 2 3

[[3]]
[1] 1 2 3

so, we can wrap it in a function;

trim <- function(xx){
  min_length <- min(sapply(xx,length))

  new_list <- lapply(xx,function(x) x[1:min_length])

  new_list  
}
user_145870410

Here is even a slightly shorter version, head directly returns the first n elements

trim<-function(x)
  lapply(x, head, n=min(lengths(x)))
list<-list(4:1,1:3,1:6)
trim(list)
#> [[1]]
#> [1] 4 3 2
#> 
#> [[2]]
#> [1] 1 2 3
#> 
#> [[3]]
#> [1] 1 2 3

Created on 2021-10-04 by the reprex package (v2.0.1)

user_74598000
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