CODEWITHSUNDEEP
r
JohnB
JohnB

Reputation: 77

R - argument length is zero

I've tried looking at other questions but none quite hits the mark. I am trying to compare two rows and depending on the result of the comparison add a number in a new column at the end of the row. I am using mtcars:

The code I use is simply this:

for (i in 1:nrow(mtcars)-1) {
    if (mtcars[i,6] > mtcars[i+1,6] ){
    mtcars[i,12] = 5
    }
}

Where col 12 is a new column. I get the following error messages: 

Error in if (mtcars[i, 6] < mtcars[i + 1, 6]) mtcars[i, 12] = 10 : argument is of length zero

There shouldn't be any null arguments so I have no clue what is returning a null argument and why this is an issue.

Thanks John

Upvotes: 0

Views: 1968

Answers (1)

Ricardo Saporta
Ricardo Saporta

Reputation: 55350

Look at 1:nrow(mtcars)-1

Compare that with 1:(nrow(mtcars)-1)
# Note the parens aroud the right-hand-side of ':'

The error comes from trying to take mtcars[0, ] which will be a zero-length vector, which in turn messes up your if clause

> 1:nrow(mtcars)-1
 [1]  0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
[25] 24 25 26 27 28 29 30 31
> 1:(nrow(mtcars)-1)
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
[25] 25 26 27 28 29 30 31

Upvotes: 2

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