# [R] How to use tapply for quantile

Patrick Hausmann patrick.hausmann at uni-bremen.de
Fri Apr 9 08:53:54 CEST 2010

```Hi James,

I don't know how to solve it with "tapply" (something with split I
think..), but you could use "plyr" (from Hadley Wickham).

library(plyr)

# Generate some data
set.seed(321)
myD <- data.frame(
Place = sample(c("AWQ","DFR", "WEQ"), 10, replace=T),
Light = sample(LETTERS[1:2], 15, replace=T),
value=rnorm(30)
)

myD[c(3,12,29), "value"] <- NA

# data.frame to data.frame
ddply(myD, .(Place, Light), summarise,
quan_value = quantile(value, na.rm=TRUE))

# data.frame to list
quant <- function(df) quantile(df\$value, na.rm=TRUE)
dlply(myD, .(Place, Light), quant)

Cheers
Patrick

Am 09.04.2010 03:24, schrieb James Rome:
> 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:
>> 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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