[R] element-by-element comparison

[Tsjerk Wassenaar]

Hi Wendy,

Most of the binary operators can deal with matrices and vectors natively:

A<-c(12,3,4)
B<-matrix(c(4,10,4,13,2,8),3,2)

B
     [,1] [,2]
[1,]    4   13
[2,]   10    2
[3,]    4    8

B<A

      [,1]  [,2]
[1,]  TRUE FALSE
[2,] FALSE  TRUE
[3,] FALSE FALSE

Cheers,

Tsjerk

On Sun, Oct 30, 2011 at 8:55 AM, Jim Lemon <jim at bitwrit.com.au> wrote:
> On 10/30/2011 02:51 PM, Wendy wrote:
>>
>> Hi,
>>
>> I have a vector and a matrix. For example,
>>
>> A = [
>> 12
>> 3
>> 4];
>>
>> B = [
>> 4       13
>> 10      2
>> 4       8];
>>
>> I am comparing A to each column of B using A>B[,ii], so the expected
>> result
>> is
>>
>> C = [
>> 1    0
>> 0    1
>> 0    0];
>>
>> I am looking for a way to do this quickly instead of going through the for
>> loop, but haven't had any luck yet? Any advice is appreciated.
>
> Hi Wendy,
> You probably mean something like this:
>
> apply(B,2,`<`,A)
>
> which means roughly
> "To each column of B, apply the function `<` using A as the comparison
> values"
>
> You will get a matrix of TRUE/FALSE values that are pretty much equivalent
> to your 0/1 values. Note that there are quite a few '*apply' functions and
> 'apply' is only guaranteed to work on arrays and matrices.
>
> Jim
>
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>



-- 
Tsjerk A. Wassenaar, Ph.D.

post-doctoral researcher
Molecular Dynamics Group
* Groningen Institute for Biomolecular Research and Biotechnology
* Zernike Institute for Advanced Materials
University of Groningen
The Netherlands