Why does times argument in rep function not behaving correctly

Question

The answer to this question maybe very simple but I cannot think of obvious reasons for this.

Why does rep(1,40*(1-0.8)) result in vector of length 7 instead of 8? Anyone please.

score 2 · Accepted Answer · answered Jan 25 '21 at 16:48

2

It's due to floating point precision:

print(40*(1-0.8), digits = 20)
## [1] 7.9999999999999982

round can be used:

rep(1, round(40*(1-0.8)))
## [1] 1 1 1 1 1 1 1 1

answered Jan 25 '21 at 16:48

G. Grothendieck

I assumed so, but I am still confused! Why 0.2*40 is not a whole number? – AnilGoyal Jan 25 '21 at 16:52
try print(1-0.8, digits = 20) – G. Grothendieck Jan 25 '21 at 16:53
1

@AnilGoyal I've marked the question as a duplicate of a FAQ - see the FAQ for a quite detailed description of why `.2 * 40` is not a whole number. – Gregor Thomas Jan 25 '21 at 16:53
1

0.2 * 40 is a whole number but 1-0.8 is not exactly 0.2 – G. Grothendieck Jan 25 '21 at 16:55

1 Answers1