[R] Aggregation across two variables in data.table

[PIKAL Petr]

Hi

Are you aware of function aggregate?

result <- with(data_tmp, aggregate(Theta, list(Marital, Education), mean))

should do the trick.

Cheers
Petr

> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Michael
> Haenlein
> Sent: Thursday, December 14, 2017 8:48 AM
> To: r-help at r-project.org
> Cc: Michael Haenlein <haenlein at escpeurope.eu>
> Subject: [R] Aggregation across two variables in data.table
>
> Dear all,
>
> I have a data.frame that includes a series of demographic variables for a
> set of respondents plus a dependent variable (Theta). For example:
>
>    Age                                Education       Marital Familysize
> Income                Housing    Theta
> 1:  50                         Associate degree      Divorced          4
>  70K+    Owned with mortgage 9.147777
> 2:  65                          Bachelor degree       Married          1
> 10-15K Owned without mortgage 7.345036
> 3:  33                          Bachelor degree       Married          2
> 30-40K    Owned with mortgage 7.974937
> 4:  69                          Bachelor degree Never married          1
>  70K+    Owned with mortgage 7.733053
> 5:  54 Some college, less than college graduate Never married          3
> 30-40K                 Rented 7.648642
> 6:  35                         Associate degree     Separated          2
> 10-15K                 Rented 7.496411
>
> My objective is to calculate the average of Theta across all pairs of two
> demographics.
>
> For 1 demographic this is straightforward:
>
> Demo_names <- c("Age", "Education", "Marital", "Familysize", "Income",
> "Housing")
> means1 <- as.list(rep(0, length(Demo_names)))
> for (i in 1:length(Demo_names)) {
> Demo_tmp <- Demo_names[i]
> means1[[i]] <- data_tmp[,list(mean(Theta)),by=Demo_tmp]}
>
> Is there an easy way to extent this logic to more than 1 variable? I know
> how to do this manually, e.g.,
> data_tmp[,list(mean(Theta)),by=list(Marital, Education)]
>
> But I don't know how to integrate this into a loop.
>
> Thanks,
>
> Michael
>
>       [[alternative HTML version deleted]]
>
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