Store values in loop into vector with seq-CodePudding

I can store values in a loop to a vector effectively when writing a loop likeso:

z = 0.5
x <- vector("numeric", 10)
for(i in 1:10){
x[i] <- z - i/10 
}
>[1]  0.4  0.3  0.2  0.1  0.0 -0.1 -0.2 -0.3 -0.4 -0.5

However, when I use a sequence of numbers instead of a colon separator likeso:

z = 0.5
x <- vector("numeric", 20)
for(i in seq(0.05, 1, 0.05)){
x[i] <- z - i
}
>[1] -0.5  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0

It fails to return me a vector for each iteration of i, why does it do this and how can I get the loop to work effectively with seq()?

CodePudding user response：

Your index also becomes a double, that's the issue. You may define a vector I with the numbers and loop over the sequence of indices. Subset both the I and the result x with i.

z <- 0.5
x <- vector("numeric", 20)
I <- seq(0.05, 1, 0.05)
for (i in seq(I)) {
  x[i] <- z - I[i]
}
x
# [1]  0.45  0.40  0.35  0.30  0.25  0.20  0.15  0.10  0.05
# [10]  0.00 -0.05 -0.10 -0.15 -0.20 -0.25 -0.30 -0.35 -0.40
# [19] -0.45 -0.50

Just in case that was not just a simplified example of something, since R is vectorized you may also do just

z - seq(0.05, 1, 0.05)
# [1]  0.45  0.40  0.35  0.30  0.25  0.20  0.15  0.10  0.05
# [10]  0.00 -0.05 -0.10 -0.15 -0.20 -0.25 -0.30 -0.35 -0.40
# [19] -0.45 -0.50