[R] Weighted descriptives by levels of another variables

David Freedman 3.14david at gmail.com
Sun Nov 15 06:08:50 CET 2009


In addition to using the survey package (and the svyby function), I've found
that many of the 'weighted' functions, such as wtd.mean, work well with the
plyr package.  For example, 

wtdmean=function(df)wtd.mean(df$obese,df$sampwt);
ddply(mydata, ~cut2(age,c(2,6,12,16)),'wtdmean')

hth, david freedman


Andrew Miles-2 wrote:
> 
> I've noticed that R has a number of very useful functions for  
> obtaining descriptive statistics on groups of variables, including  
> summary {stats}, describe {Hmisc}, and describe {psych}, but none that  
> I have found is able to provided weighted descriptives of subsets of a  
> data set (ex. descriptives for both males and females for age, where  
> accurate results require use of sampling weights).
> 
> Does anybody know of a function that does this?
> 
> What I've looked at already:
> 
> I have looked at describe.by {psych} which will give descriptives by  
> levels of another variable (eg. mean ages of males and females), but  
> does not accept sample weights.
> 
> I have also looked at describe {Hmisc} which allows for weights, but  
> has no functionality for subdivision.
> 
> I tried using a by() function with describe{Hmisc}:
> 
> by(cbind(my, variables, here), division.variable, describe,  
> weights=weight.variable)
> 
> but found that this returns an error message stating that the  
> variables to be described and the weights variable are not the same  
> length:
> 
> Error in describe.vector(xx, nam[i], exclude.missing =  
> exclude.missing,  :
>    length of weights must equal length of x
> In addition: Warning message:
> In present & !is.na(weights) :
>    longer object length is not a multiple of shorter object length
> 
> This comes because the by() function passes down a subset of the  
> variables to be described to describe(), but not a subset of the  
> weights variable.  describe() then searches the whatever data set is  
> attached in order to find the weights variables, but this is in its  
> original (i.e. not subsetted) form.  Here is an example using the  
> ChickWeight dataset that comes in the "datasets" package.
> 
> data(ChickWeight)
> attach(ChickWeight)
> library(Hmisc)
> #this gives descriptive data on the variables "Time" and "Chick" by  
> levels of "Diet")
> by(cbind(Time, Chick), Diet, describe)
> #trying to add weights, however, does not work for reasons described  
> above
> wgt=rnorm(length(Chick), 12, 1)
> by(cbind(Time, Chick), Diet, describe, weights=wgt)
> 
> Again, my question is, does anybody know of a function that combines  
> both the ability to provided weighted descriptives with the ability to  
> subdivide by the levels of some other variable?
> 
> 
> Andrew Miles
> Department of Sociology
> Duke University
> 
> 
> 
> 
> 	[[alternative HTML version deleted]]
> 
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