Sampling a vector by equal split

Question

If I have a vector of strings of any length say;

vec <- c("a","b","c","d","e","f","g","h","i")

I am looking for a function to sample n number of values from this vector using a strategy shown below. Showing figures since it's hard to explain.

function call: 
result:
schematic diagram:

fn(vector=vec,n=1)
"a"

|
a b c d e f g h i


fn(vector=vec,n=2)
"a" "i"
 _______________
|               |
a b c d e f g h i


fn(vector=vec,n=3)
"a" "e" "i"
 _______________
|       |       |
a b c d e f g h i


fn(vector=vec,n=4)
"a" "c" "g" "i"
 _______________
|   |     |     |
a b c d e f g h i


fn(vector=vec,n=5)
"a" "c" "e" "g" "i"
 _______________
|   |   |   |   |
a b c d e f g h i

The sampling does not have to be accurate. The values can be from roughly the correct region but must be consistent. The string vector can be even or odd.

Answer 1

One way would be to use seq(), taking advantage of it's length.out= argument to get the evenly spaced indices that you seek:

fn <- function(x, n) {
    x[round(seq(1,length(x), length.out=n))]
}

## Check that it works
fn(vec, 1)
# [1] "a"
fn(vec, 2)
# [1] "a" "i"
fn(vec, 4)
# [1] "a" "d" "f" "i"
fn(vec, 8)
# [1] "a" "b" "c" "d" "f" "g" "h" "i"