[R] OK, next Q - a sort of factorial on a vector

[Philip Rhoades]

Ivan,


On 2023-06-21 03:32, Ivan Krylov wrote:
> В Wed, 21 Jun 2023 03:13:52 +1000
> Philip Rhoades via R-help <r-help using r-project.org> пишет:
> 
>> This:
>> 
>>    !(1,2,3,4,5)
>> 
>> would give this:
>> 
>>    (2,3,4,5, 6,8,10, 12,15, 20)
> 
> Do you mean taking a product of every element of the vector with all
> following vector elements? A relatively straightforward way would be
> (given your vector stored in `x`):
> 
> unlist(lapply(seq_along(x), function(i) x[i] * x[-(1:i)]))


Perfect!


> (I'm sure it could be golfed further.)


I will look at Sarah's suggestion too.


>> and this:
>> 
>>    !(1,2,NA,4,5)
>> 
>> would give this:
>> 
>>    (2,4,5, 8,10, 20)
> 
> The previous solution seems to give your vector interspersed a bunch of
> NAs, so one way to continue would be to filter it using v[!is.na(v)].


Exactly!

Thanks people - it would have taken forever to work that out myself (it 
has been decades since I looked at R).

Phil.
-- 
Philip Rhoades

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E-mail:  phil using pricom.com.au