[R] Count of unique factors within another factor

[Charles C. Berry]

On Sun, 13 Jun 2010, Birdnerd wrote:

>
> I have a data frame with two factors (sampling 'unit', 'species'). I want to
> calculate the number of unique 'species' per 'unit.' I can calculate the
> number of unique values for each variable separately, but can't get a count
> for each ‘unit’.
>

If I understand you

 	colSums( xtabs( ~ specie + unit , data ) !=0 )

HTH,

Chuck

>> data=read.csv("C:/Desktop/sr_sort_practice.csv")
>> attach(data)
>
>> data[1:10,]
>   unit species
> 1   123    ACMA
> 2   123    LIDE
> 3   123    LIDE
> 4   123    SESE
> 5   123    SESE
> 6   123    SESE
> 7   345    HEAR
> 8   345    LOHI
> 9   345    QUAG
> 10  345    TODI…..
>
>> sr.unique<- lapply (data, unique)
> $unit
> [1] 123 345 216
> $species
> [1] ACMA  LIDE  SESE  HEAR  LOHI  QUAG  TODI  UMCA  ARSP  LIDE
>
>> sapply (sr.unique,length)
>    unit species
>      3      10
>
> Then, I get stuck here because this unique species count is not given for
> each ‘unit’.
> What I'd like to get is:
>
> unit species
> 123    3
> 345    4
> 216    --
>
> Thanks--
>
> -- 
> View this message in context: http://r.789695.n4.nabble.com/Count-of-unique-factors-within-another-factor-tp2253545p2253545.html
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>
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Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901