CODEWITHSUNDEEP
r
Ben
Ben

Reputation: 6741

How to modify vector elements by a function depending on the element index in R?

Suppose I have a vector:

my.vector <- rep(0, length.out = 100)

I want to modify each element of the vector by a new value depending on the element index.

Of course, I can use a for loop:

for(i in 1:length(my.vector)) {
  my.vector[[i]] <- my.vector[[i]] + i * 0.25
}

But I'm sure there are better ways to do this in R.

With sapply?

sapply(seq_along(my.vector), function(i) my.vector[[i]] + i * 0.25)

OK, I get the same result, but it's less readable. Do you know of other cleaner ways?

Upvotes: 0

Views: 54

Answers (3)

akrun
akrun

Reputation: 886938

We can use seq_along

my.vector + seq_along(my.vector) *0.25

Upvotes: 1

lmo
lmo

Reputation: 38500

There are a large number of ways to approach this. One of the canonical methods uses seq:

myVectorSeq <- my.vector + seq(.25, 25, length.out=length(my.vector))

You can accomplish @lorenzo-rossi's method using seq_len:

myVectorSeq <- my.vector + (seq_len(length(my.vector)) * .25)

seq_len, which is faster than the more flexible seq function.

Upvotes: 1

Lorenzo Rossi
Lorenzo Rossi

Reputation: 1481

Simply create a new vector and then use a vectorized sum:

sums_vec = (1:length(my.vector)) * 0.25
my.vector + sums_vec

Upvotes: 1

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