Fill vector with sequence

Question

Can you explain me, why, when i fill vector in R with sequence, i ve got this result:

sekv <- seq(from = 1, to = 20, by = 2)
test <- c()
for (j in sekv) {
    test[j] = j
}
test
[1]  1 NA  3 NA  5 NA  7 NA  9 NA 11 NA 13 NA 15 NA 17 NA 19

I want make a vector, which i can fill with some sequence and use it in loop, but only with values, not with NA values. Can somebody help me ?

Answer 1

In sekv you currently pass 2.. 4 ..6, use seq_along

   sekv <- seq(from = 1, to = 20, by = 2)
    test <- c()
    for (j in seq_along(sekv)) {
      test[j] = j
    }
     test

Answer 2

The reason why you have NAs in the test vector is that you assign the first, third, fifth, seventh, etc element in the test vector to be 1, 3, 5, 7 etc...

I am still not very clear what you are trying to do, but one solution is that you can remove all the NAs after the for loop.

sekv <- seq(from = 1, to = 20, by = 2)
test <- c()
for (j in sekv) {
  test[j] = j
}
test
# [1]  1 NA  3 NA  5 NA  7 NA  9 NA 11 NA 13 NA 15 NA 17 NA 19
test <- test[-c(which(is.na(test)))]
test
# [1]  1  3  5  7  9 11 13 15 17 19

As @PoGibas suggested, this also works if you want to remove NAs:

test <- na.omit(test) 
test
# [1]  1  3  5  7  9 11 13 15 17 19

Answer 3

The actual issue is that whenever your are trying to assign value to test[j] it using value of j to change the size of the vector. The last value of j is 19 hence size of test is set to 19. But you have assigned value only to few indexes ie 1, 3, 5 etc. Rest of values are set to NA.

You can solve it by executing for loop only for number of items available in sekv .

sekv <- seq(from = 1, to = 20, by = 2)
test <- c()
for (j in 1:length(sekv)) {
    test[j] = sekv[j]
}
print(test)