[R] count data with some conditions

[David Winsemius]

On Nov 1, 2008, at 3:30 AM, (Ted Harding) wrote:

> On 01-Nov-08 02:51:37, David Winsemius wrote:
>> Do you want the count of remaining  elements which are strictly
>> greater than the first element?
>>
>>> length(which(a[1] < a[2:10]))
>> [1] 4
>>
>> or perhaps a bit more deviously:
>>
>>> sum( a[1]<a[2:10]+0 ) #adding 0 to TRUE or FALSE creates 1 or 0.
>> [1] 4
>
> No need to be devious! Simply
>  sum(a[1] < a[2:10])
> # [1] 4
> will do it. The reason is that when TRUE or FALSE are involved in
> an arithmetic operation (which sum() is), they are cast into 1 or 0.

Agreed. I now also see that TRUE+TRUE and T+T both return 2. The  
second observation should be further warning to us newbies not to  
create variables named "T".

It's now been pointed out to me both on and off list that the +0 is  
unnecessary. I don't remember when I learned this, but it could not  
have been more than a year ago. I seem to remember that Gabor  
Grothendeick used the +0 device to convert a logical vector to a  
numeric vector. Perhaps it was for the purpose of making a matrix or  
something less necessarily arithmetical than sum() or "+".

-- 
David Winsemius, MD
Heritage Labs
>
>
> Ted.
>
>> On Oct 31, 2008, at 7:56 PM, sandsky wrote:
>>> Hi there,
>>> I have a data set:
>>>
>>> a=cbind(5,2,4,7,8,3,4,11,1,20)
>>>
>>> I want to count # of data, satistfying a[1]<a[2:10].
>>> Anyone helps me solving this case?
>>>
>>> Thank you in advance,
>>> Jin
>
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> E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
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> Date: 01-Nov-08                                       Time: 07:30:17
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