[R] combining columns into a "combination index" of the same length

[Emmanuel Levy]

Thanks Thierry, you made my day :)


On 21 July 2015 at 17:00, Thierry Onkelinx <thierry.onkelinx at inbo.be> wrote:

> Please always keep the mailing list in cc.
>
> If mat is a data.frame, then you can use do.call. Then the number of
> columns doesn't matter.
>
> do.call(paste, mtcars[, c("mpg", "cyl")])
> do.call(paste, mtcars[, c("mpg", "cyl", "disp")])
> do.call(paste, mtcars)
>
>
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek / Research Institute for Nature and
> Forest
> team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
> Kliniekstraat 25
> 1070 Anderlecht
> Belgium
>
> To call in the statistician after the experiment is done may be no more
> than asking him to perform a post-mortem examination: he may be able to say
> what the experiment died of. ~ Sir Ronald Aylmer Fisher
> The plural of anecdote is not data. ~ Roger Brinner
> The combination of some data and an aching desire for an answer does not
> ensure that a reasonable answer can be extracted from a given body of data.
> ~ John Tukey
>
> 2015-07-21 15:43 GMT+02:00 Emmanuel Levy <emmanuel.levy at gmail.com>:
>
>> Thanks! -- this is indeed much faster (plus I made a mistake, one has to
>> use paste with the option collapse="".
>>
>> The thing is I'm looking for a solution *without paste*. The reason is
>> that* there may be two or more columns*.
>>
>>
>>
>> On 21 July 2015 at 16:32, Thierry Onkelinx <thierry.onkelinx at inbo.be>
>> wrote:
>>
>>> Yes. paste0() can work on vectors. So paste0(mat[, col1], mat[, col2])
>>>
>>> ir. Thierry Onkelinx
>>> Instituut voor natuur- en bosonderzoek / Research Institute for Nature
>>> and Forest
>>> team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
>>> Kliniekstraat 25
>>> 1070 Anderlecht
>>> Belgium
>>>
>>> To call in the statistician after the experiment is done may be no more
>>> than asking him to perform a post-mortem examination: he may be able to say
>>> what the experiment died of. ~ Sir Ronald Aylmer Fisher
>>> The plural of anecdote is not data. ~ Roger Brinner
>>> The combination of some data and an aching desire for an answer does not
>>> ensure that a reasonable answer can be extracted from a given body of data.
>>> ~ John Tukey
>>>
>>> 2015-07-21 15:21 GMT+02:00 Emmanuel Levy <emmanuel.levy at gmail.com>:
>>>
>>>> Hi,
>>>>
>>>> The answer to this is probably straightforward, I have a dataframe and
>>>> I'd
>>>> like to build an index of column combinations, e.g.
>>>>
>>>> col1 col2  --> col3 (the index I need)
>>>> A     1           1
>>>> A     1           1
>>>> A     2           2
>>>> B     1           3
>>>> B     2           4
>>>> B     2           4
>>>>
>>>>
>>>> At the moment I use:
>>>> col3 <- apply(mat[,sel.col], 1, paste0)
>>>>
>>>> But I wonder if another approach could be faster?
>>>>
>>>> Thanks,
>>>>
>>>> Emmanuel
>>>>
>>>>         [[alternative HTML version deleted]]
>>>>
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>>>
>>>
>>
>

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