Converting long to wide format

Question

id <- c(1:8,1:8)
age1 <- c(7.5,6.7,8.6,9.5,8.7,6.3,9,5)
age2 <- age1 + round(runif(1,1,3),1)
age <- c(age1, age2)

tanner <-  sample(1:2, 16,replace=T)

d         


        

Answer 1

We can use dcast to convert from 'long' to 'wide' and use the fun.aggregate as min. Here I converted the 'data.frame' to 'data.table' (setDT(df)) as the dcast from data.table would be fast.

library(data.table)
res <- dcast(setDT(df), id~paste('age',tanner,sep='.'), value.var='age', min)
res
#   id age.1 age.2
#1:  1  10.0   7.5
#2:  2   6.7   Inf
#3:  3  11.1   8.6
#4:  4   Inf   9.5
#5:  5   8.7  11.2
#6:  6   6.3   8.8
#7:  7   9.0   Inf
#8:  8   5.0   Inf

If we want to change the 'Inf' to 'NA'

res[,(2:3) := lapply(.SD, function(x)
          replace(x, is.infinite(x), NA)),.SDcols= 2:3]