[R] behavior of "by"

[Rolf Turner]

On 29/10/2008, at 2:04 PM, Jeff Laake wrote:

> Any insight into the behavior of "by" in the following case would be
> appreciated.  There is a note in the help details for "by" about
> documenting behavior since v2.7 but I don't entirely understand  
> what it
> is saying.  I'm using R2.7.2 Windows.  I'm interested if the following
> behavior was a change or whether it has always worked this way.  I
> looked at RSiteSearch and read through version changes but found  
> nothing.
>
> Take a dataframe as follows:
>> samples
>    Region.Label  Area Sample.Label Effort Label
> 1             1 10000            1    100    11
> 2             1 10000            2    100    12
> 3             1 10000            3    100    13
> 4             1 10000            4    100    14
> 5             1 10000            5    100    15
> 6             1 10000            6    100    16
> 7             1 10000            7    100    17
> 8             1 10000            8    100    18
> 9             1 10000            9    100    19
> 10            1 10000           10    100   110
>
> Use "by" to tally number of entries with particular values of
> Region.Label (in this case there is only 1 value of Region.Label)
>
> by(samples$Effort,samples$Region.Label,length)
> INDICES: 1
> [1] 1
>
> I expected to get 10 instead of 1.


	<snip>

Cannot reproduce the problem:

  > samples
    Region.Label  Area Sample.Label Effort Label
1             1 10000            1    100    11
2             1 10000            2    100    12
3             1 10000            3    100    13
4             1 10000            4    100    14
5             1 10000            5    100    15
6             1 10000            6    100    16
7             1 10000            7    100    17
8             1 10000            8    100    18
9             1 10000            9    100    19
10            1 10000           10    100   110
  > by(samples$Effort,samples$Region.Label,length)
samples$Region.Label: 1
[1] 10

I.e. I get 10 as you expected.

	cheers,

		Rolf Turner

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