CODEWITHSUNDEEP
rloopsapply
tv box
tv box

Reputation: 1

Using apply or a loop to output a vector with predetermined length

I need to repeat the following a process like this 10 times:

> random=rnorm(5)  
> total=sum(random)

and then put the total each time into a vector called final.

For a loop I guess I would write:

> final <- c(total[[i]])
> for(i in 1:10){  
  random=rnorm(5)  
  total=sum(random)
  ...
}

...not sure how to put my totals into my final vector? Also from looking around online most places say I should use an apply code. Which should I use and how can I put the totals into final?

Upvotes: 0

Views: 301

Answers (1)

user295691
user295691

Reputation: 7248

R provides a function called replicate for exactly this use case, it will repeat the operation as many times as you specify, and store the results in a vector:

> replicate(10, sum(rnorm(5)))
[1] -0.2286870  1.5123902 -5.8179539  1.2119908 -2.8749987  5.5817021
[7]  2.5427969  2.1833426  0.4884455 -3.6787912

If the function to produce data is more complex, then you can either use replicate to invoke a function, or use sapply directly. So

> genRandomData <- function() {
    random <- rnorm(100)
    c(sum(random), var(random))
}
> replicate(10, genRandomData())
         [,1]     [,2]      [,3]      [,4]      [,5]      [,6]       [,7]
[1,] 6.612235 6.895032 -4.004501 -8.250871 2.3098680 2.0388161 23.5202949
[2,] 1.082576 0.769107  1.119480  1.206932 0.9930102 0.9078762  0.9544335
            [,8]      [,9]     [,10]
[1,] -12.2080648 9.0074524 0.2358715
[2,]   0.8256081 0.8669045 0.9017415

or, to produce the same output using sapply (which is nice because it doesn't reply on substitution),

> sapply(integer(10), function(x) {
    random <- rnorm(100)
    c(sum(random),var(random))
})

If you want to get a data frame out of the end of this, you have to transpose; so

> data.frame(t(sapply(integer(10), function(x) {
    random <- rnorm(100)
    list(s=sum(random),v=var(random))
})))
            s         v
1   -6.343845    1.0397
2    12.94773 0.9480807
3    5.811322 0.9670198
4   -1.941444   1.04547
5  -0.9094589  0.862759
6   -2.852641 0.5504582
7   -8.471266  1.080554
8    -17.2341  1.201679
9    11.60805  1.150254
10  -7.138314  1.080731

Upvotes: 2

Related Questions