Question

I would like to create a numeric vector with the results of a loop such as

> for (i in 1:5) print(i+1)
[1] 2
[1] 3
[1] 4
[1] 5
[1] 6

It seems strange that the same expression without ‘print’ returns nothing

> for (i in 1:5) i+1
>

Does anyone have an explanation/solution?

Answer 1

This is standard behaiviour — when you say you want to create a numeric vector,
print will not do that

The expression in a for loop is an argument to the primitive function for

From ?`for` in the value section

for, while and repeat return NULL invisibly. for sets var to the last
used element of seq, or to NULL if it was of length zero.

print prints the results to the console.

for(i in 1:5) i + 1

merely calculates i + 1 for each iteration and returns nothing

If you want to assign something then assign it using <-, or less advisably assign

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You can avoid an explicit loops by using sapply. This (should) avoid any pitfalls of growing vectors

results <- sapply(1:5, function(i) { i + 1})