CODEWITHSUNDEEP
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Diego F. Rodríguez V.
Diego F. Rodríguez V.

Reputation: 238

Inconsistent behavior of : operator

I was trying to create a sequence of odd values using the : operator (like in Octave), when I ran into a weird behavior.

I tried the same operation with different values.

> 1:2:10
 [1]  1  2  3  4  5  6  7  8  9 10
Warning message:
In 1:2:10 : numerical expression has 2 elements: only the first used
> 1:0.2:10
 [1]  1  2  3  4  5  6  7  8  9 10
> 1:0.5:10
 [1]  1  2  3  4  5  6  7  8  9 10
> 1:0.9:10
 [1]  1  2  3  4  5  6  7  8  9 10
> 1:1.9:10
 [1]  1  2  3  4  5  6  7  8  9 10
> 1:2.9:10
 [1]  1  2  3  4  5  6  7  8  9 10
Warning message:
In 1:2.9:10 : numerical expression has 2 elements: only the first used
> 1:3.9:10
 [1]  1  2  3  4  5  6  7  8  9 10
Warning message:
In 1:3.9:10 : numerical expression has 3 elements: only the first used

I don't understand the difference. I would like to know why sometimes I get a warning and other times not and the difference in warning messages. I know I have to use seq to get the odd values I wanted, but this inconsistent behavior puzzles me.

Upvotes: 2

Views: 54

Answers (1)

markus
markus

Reputation: 26363

When you do

1:1.9

the result is

# 1

and so 1:1.9:10 is the same as 1:10.

But when you call

1:2

you get

# 1 2

Hence 1:2:10 is the same as calling

c(1, 2):10 # which gives 1:10 see warning
# [1]  1  2  3  4  5  6  7  8  9 10
#Warning message:
#In c(1, 2):10 : numerical expression has 2 elements: only the first used

From the help page:

Arguments

from : starting value of sequence.

to : (maximal) end value of the sequence.

...

Value to will be included if it differs from from by an integer up to a numeric fuzz of about 1e-7.

Upvotes: 6

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