[R] count() function

[Christopher R. Dolanc]

Yes, I just tried the length() function and it worked beautifully.

Thank you.

On 4/5/2012 6:01 PM, William Dunlap wrote:
> I think you are looking for the function called length().  I cannot recreate
> your output, since I don't know what is in NZ_Conifers, but with the built-in
> dataset mtcars I get:
>
>    >  ddply(mtcars, .(cyl,gear,carb), summarize, MeanWt=mean(wt), N=length(wt))
>       cyl gear carb  MeanWt N
>    1    4    3    1 2.46500 1
>    2    4    4    1 2.07250 4
>    3    4    4    2 2.68375 4
>    4    4    5    2 1.82650 2
>    5    6    3    1 3.33750 2
>    6    6    4    4 3.09375 4
>    7    6    5    6 2.77000 1
>    8    8    3    2 3.56000 4
>    9    8    3    3 3.86000 3
>    10   8    3    4 4.68580 5
>    11   8    5    4 3.17000 1
>    12   8    5    8 3.57000 1
>    >  with(mtcars, sum(cyl==8&  gear==3&  carb==4)) # output line 10
>    [1] 5
>
> If all you want is the count of things in various categories, you can use table
> instead of ddply and length:
>    >  with(mtcars, table(cyl, gear, carb))
>    , , carb = 1
>
>       gear
>    cyl 3 4 5
>      4 1 4 0
>      6 2 0 0
>      8 0 0 0
>
>    , , carb = 2
>
>       gear
>    cyl 3 4 5
>      4 0 4 2
>      6 0 0 0
>      8 4 0 0
>    ...
>
> Using ftable on table's output gives a nicer looking printout, but table's output is easier
> to use in a program.
>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
>
>> -----Original Message-----
>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
>> Of Christopher R. Dolanc
>> Sent: Thursday, April 05, 2012 12:16 PM
>> To: r-help at r-project.org
>> Subject: [R] count() function
>>
>> I keep expecting R to have something analogous to the =count function in
>> Excel, but I can't find anything. I simply want to count the data for a
>> given category.
>>
>> I've been using the ddply() function in the plyr package to summarize
>> means and st dev of my data, with this code:
>>
>> ddply(NZ_Conifers,.(ElevCat, DataSource, SizeClass), summarise,
>> avgDensity=mean(Density), sdDensity=sd(Density), n=sum(Density))
>>
>> and that gives me results that look like this:
>>
>>      ElevCat DataSource SizeClass avgDensity   sdDensity            n
>> 1    Elev1        FIA    Class1   38.67768  46.6673478    734.87598
>> 2    Elev1        FIA    Class2   27.34096  23.3232470    820.22879
>> 3    Elev1        FIA    Class3   15.38758   0.7088432     76.93790
>> 4    Elev1        VTM    Class1   66.37897  70.2050817  24958.49284
>> 5    Elev1        VTM    Class2   39.40786  34.9343269  11782.95152
>> 6    Elev1        VTM    Class3   21.17839  12.3487600   1461.30895
>>
>> But, instead of "sum(Density)", I'd really like counts of "Density", so
>> that I know the sample size of each group. Any suggestions?
>>
>> --
>> Christopher R. Dolanc
>> Post-doctoral Researcher
>> University of California, Davis
>>
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>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.

-- 
Christopher R. Dolanc
Post-doctoral Researcher
University of California, Davis