CODEWITHSUNDEEP
rlistvectorappendsapply
Rachit Agrawal
Rachit Agrawal

Reputation: 3343

R + combine a list of vectors into a single vector

I have a single list of numeric vector and I want to combine them into one vector. But I am unable to do that. This list can have one element common across the list element. Final vector should not add them twice. Here is an example:

>lst
`1`
[1] 1 2
`2`
[2] 2 4 5
`3`
[3] 5 9 1

I want final result as this

>result
[1] 1 2 4 5 9 1

I tried doing following things, without worrying about the repition:

>vec<-vector()
>sapply(lst, append,vec)

and

>vec<-vector()
>sapply(lst, c, vec)

None of them worked. Can someone help me on this?

Thanks.

Upvotes: 66

Views: 73367

Answers (6)

Prradep
Prradep

Reputation: 5696

Benchmarking the two answers by Rachit and Martijn

rbenchmark::benchmark(
  "unlist" = {
    vec<-unlist(a)
    vec[which(diff(vec) != 0)]
  },
  "reduce" = {
    a %>% reduce(c) %>% unique
  }
)

Output:

    test replications elapsed relative user.self sys.self user.child sys.child
2 reduce          100   0.036        3     0.036    0.000          0         0
1 unlist          100   0.012        1     0.000    0.004          0         0

This one clearly beat the other one.

Upvotes: 4

Rachit Agrawal
Rachit Agrawal

Reputation: 3343

A solution that is faster than the one proposed above:

vec<-unlist(lst)
vec[which(c(1,diff(vec)) != 0)]

Upvotes: 64

MartijnVanAttekum
MartijnVanAttekum

Reputation: 1435

Doing it the tidyverse way:

library(tidyverse)
lst %>% reduce(c) %>% unique

This uses the (uncapitalized) reduce version from purrr in combination with pipes. Also note that if the list contains named vectors, the final naming will be different depending on whether unlist or reduce methods are used.

Upvotes: 3

Paul Rougieux
Paul Rougieux

Reputation: 11379

Another answer using Reduce().

Create the list of vectors:

lst <- list(c(1,2),c(2,4,5),c(5,9,1))

Combine them into one vector

vec <- Reduce(c,lst)
vec
# [1] 1 2 2 4 5 5 9 1

Keep the repeated ones only once:

unique(Reduce(c,lst))
#[1] 1 2 4 5 9

If you want to keep that repeated one at the end, You might want to use vec[which(c(1,diff(vec)) != 0)] as in @Rachid's answer

Upvotes: 27

0mn1
0mn1

Reputation: 156

stack will do this nicely too, and looks more concise:

stack(lst)$values

Upvotes: 7

Matthew Lundberg
Matthew Lundberg

Reputation: 42629

You want rle:

rle(unlist(lst))$values

> lst <- list(`1`=1:2, `2`=c(2,4,5), `3`=c(5,9,1))
> rle(unlist(lst))$values
## 11 21 22 31 32 33 
##  1  2  4  5  9  1

Upvotes: 8

Related Questions