[R] How to use tapply for quantile

[Charles C. Berry]

On Thu, 8 Apr 2010, James Rome wrote:

> I am trying to calculate quantiles of a data frame column split up by
> two factors:
> # Calculate the quantiles
>    quarts = tapply(gdf$tt, list(gdf$Runway, gdf$OnHour), FUN=quantile,
> na.rm = TRUE)
> This does not work:


It seems like it did work. It returned a matrix list of the results, some 
of which are NULL and some of which are numeric vectors of length 5.

Try

 	str( quarts )

to get a sense of what is going on.

HTH,

Chuck

p.s.  providing commented, minimal, self-contained, reproducible code (as 
requested) will give you more informative answers.

>> quarts
>   04L       04R       15R       22L       22R       27        32
> 33L       33R
> 0  NULL      Numeric,5 NULL      Numeric,5 NULL      Numeric,5 NULL
> Numeric,5 NULL
> 1  NULL      Numeric,5 NULL      Numeric,5 NULL      NULL      NULL
> Numeric,5 NULL
> 2  NULL      NULL      NULL      Numeric,5 NULL      NULL      NULL
> NULL      NULL
> 3  NULL      NULL      NULL      NULL      NULL      NULL      NULL
> Numeric,5 NULL
> 4  NULL      NULL      NULL      NULL      NULL      NULL      NULL
> NULL      NULL
> 5  NULL      NULL      NULL      NULL      NULL      NULL      NULL
> NULL      NULL
> 6  NULL      NULL      NULL      NULL      NULL      NULL      NULL
> NULL      NULL
> 7  NULL      Numeric,5 NULL      NULL      NULL      Numeric,5 NULL
> Numeric,5 NULL
> 8  NULL      Numeric,5 NULL      Numeric,5 NULL      Numeric,5 NULL
> Numeric,5 NULL
> . . .
>
> But if I leave out either of the two factors, it does work
>> quarts = tapply(gdf$tt, list(gdf$Runway), FUN=quantile, na.rm = TRUE)
>> quarts
> $`04L`
>  0%  25%  50%  75% 100%
>   4    8    9   10   20
>
> $`04R`
>  0%  25%  50%  75% 100%
>   0    9   10   11   28
> . . . .
>
> How can I get this to work?
>
> Thanks,
> Jim Rome
>
> ______________________________________________
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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.
>

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