[R] "By" function Frame Conversion (with Multiple Indices)

[David Winsemius]

On Jan 3, 2013, at 9:00 PM, Ray DiGiacomo, Jr. wrote:

> Hello,
>
> I have the following dataset.  Please note that there are missing  
> values on
> records 4 and 5:
>
> id,age,weight,height,gender
> 1,22,180,72,m
> 2,13,100,67,f
> 3,5,40,40,f
> 4,6,42,,f
> 5,12,98,66,
> 6,50,255,60,m
>
> I'm using the "By" function like this:
>
> list1 <- by(dataset[c("weight", "height")],
>             dataset[c("age", "gender")],
>             colMeans,
>                          na.rm = TRUE)

I named the dataframe "dat"

aggregate( dat[,c("weight", "height")],
              list( age=dat$age, gender=dat$gender), FUN=mean,  
na.rm=TRUE)
   age gender weight height
1  12            98     66
2   5      f     40     40
3   6      f     42    NaN
4  13      f    100     67
5  22      m    180     72
6  50      m    255     60

-- 
David.
>
> I then convert the list above to a frame like this:
>
> as.data.frame( do.call(rbind, list1) )
>
> I get this output from the code above:
>
>    weight height
> 1     40     40
> 2     42    NaN
> 3    100     67
> 4    180     72
> 5    255     60
>
> I want to get the output above, but I also want two additional columns
> named "age" and "gender" (with the age and gender values from the "By"
> function output).
>
> How would I do this?
>
> Best Regards,
>
> Ray DiGiacomo, Jr.
> Healthcare Predictive Analytics Specialist
> President, Lion Data Systems LLC
> President, The Orange County R User Group
> Board Member, TDWI
> rayd at liondatasystems.com
> (m) 408-425-7851
> San Juan Capistrano, California USA
> twitter.com/liondatasystems
> linkedin.com/in/raydigiacomojr
> youtube.com/user/liondatasystems/videos
> liondatasystems.com/courses
>
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>
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David Winsemius, MD
Alameda, CA, USA