CODEWITHSUNDEEP
r
Tamas
Tamas

Reputation: 776

R, sapply does not seem to apply the function provided

Looking into the apply function family, sapply does not produce what I would like to. The problem I simplified to a basic example below. I create a vector and then perform a sum operation.

1.
v<-c(1:9)
sum(v)
#this returns 45 as expected

2.
sapply (v, sum)
#this returns [1] 1 2 3 4 5 6 7 8 9

How should I use sapply() to sum the vector above? Thanks a lot.

Upvotes: 0

Views: 387

Answers (3)

Bruce Schardt
Bruce Schardt

Reputation: 210

you would use the reduce functional in this case

    v<-c(1:9)
    sum(v)
    #this returns 45 as expected

    purrr::reduce(v,sum)
    #this also returns 45

    # or base R
    Reduce(sum,v)
    # this also returns 45

Upvotes: 0

Hector Haffenden
Hector Haffenden

Reputation: 1369

If you must use sapply, try,

sapply (list(v), sum)
[1] 45

The function sapply applies the function sum to each element. So for the vector v, it was summing up each individual element.

It is clear the sum of one element, is that element.

Using the list function, we them apply the sum function to the first element of the list, which is v, giving the desired result.

Just for understanding, we can use any function to move the vector "down a level", like data.frame,

> sapply(data.frame(v), sum)[[1]]
[1] 45

But in your case, there is no need for sapply.

Upvotes: 2

divibisan
divibisan

Reputation: 12155

sapply applies a function to each element of a list. So what you're doing here is applying sum to each number on its own – which doesn't accomplish anything. You can see what's happening in this example:

sapply(1:9, function(x) x + 1)
[1]  2  3  4  5  6  7  8  9 10

Using sum with apply only makes sense if you want to sum multiple elements of a list:

sapply(list(1:9, 3:4), sum)
[1] 45  7

Here, sum is applied to each vector in the list

Upvotes: 3

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