Aggregate data vectors by group

TODO

• link to dfAggregate, dfAggregate_tidy

Separate descriptive statistics for each group

Njk   <- 2
P     <- 2
Q     <- 3
IQ    <- round(rnorm(Njk*P*Q, mean=100, sd=15))
sex   <- factor(rep(c("f", "m"),       times=Q*Njk))
group <- factor(rep(c("T", "WL", "CG"), each=P*Njk))
table(sex, group)

   group
sex CG T WL
  f  2 2  2
  m  2 2  2

tapply()

tapply(IQ, group, FUN=mean)

    CG      T     WL 
 90.75 102.00 102.25 

tapply(IQ, list(sex, group), FUN=mean)

    CG   T    WL
f 97.5  98  94.5
m 84.0 106 110.0

ave()

ave(IQ, sex, FUN=mean)

 [1]  96.66667 100.00000  96.66667 100.00000  96.66667 100.00000  96.66667
 [8] 100.00000  96.66667 100.00000  96.66667 100.00000

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