R help - May 2011 - What does "smaller than" comparison do on strings?

What's the logic behind the following, and where can I find any 
documentation about it? In particular, why are 2:9 - as characters - not 
regarded as being smaller than 10?

# R-Code:
a <- as.character(1:12)

a < 10
#  [1]  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE 
FALSE

Thanks in advance!

Niklaus

On 25/05/2011 6:06 AM, Niklaus Kuehnis wrote:
> What's the logic behind the following, and where can I find any
> documentation about it? In particular, why are 2:9 - as characters - not
> regarded as being smaller than 10?
>
> # R-Code:
> a<- as.character(1:12)
>
> a<  10
> #  [1]  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
> FALSE
See ?Comparison for help.  There are lots of details given there.

In summary:  your second comparison is of "2" to "10". 
Since the
character "2" sorts later than the character "1",
"2" < "10" is FALSE.

Duncan Murdoch

Hi:

Here are two alternatives that do work as you expect; sprintf() is your friend:
> sprintf("%2d", 1:12)
 [1] " 1" " 2" " 3" " 4" " 5"
" 6" " 7" " 8" " 9" "10"
"11" "12"
> sprintf("%02d", 1:12)
 [1] "01" "02" "03" "04" "05"
"06" "07" "08" "09" "10"
"11" "12"
> sprintf("%2d", 1:12) < 10
 [1]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE
FALSE
> sprintf("%02d", 1:12) < 10
 [1]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE FALSE

A leading space or leading 0 on the digits 1-9 'fixes' the problem for
the reason Duncan mentioned.

HTH,
Dennis

On Wed, May 25, 2011 at 3:06 AM, Niklaus Kuehnis
<kuehnik_0505 at gmx-topmail.de> wrote:
> What's the logic behind the following, and where can I find any
> documentation about it? In particular, why are 2:9 - as characters - not
> regarded as being smaller than 10?
>
> # R-Code:
> a <- as.character(1:12)
>
> a < 10
> # ?[1] ?TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
> FALSE
>
> Thanks in advance!
>
> Niklaus
>
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