How to create missing value for repeated measurement data?

Question

I have a data set that not every subject’s observations were observed at the exact same time points, but I want to turn it in to a data set that every one’s observations wer

Answer 1

Using tidyr, this is a one liner. You use the complete function, which creates rows with each combination of the columns passed to it, filling the rest of the rows with NA:

library(tidyr)
complete(m, id, age)

Source: local data frame [18 x 3]

      id   age    IQ
   (dbl) (dbl) (dbl)
1      1     2     3
2      1     3     4
3      1     4     5
4      1     5     4
5      1     6    NA
6      1     8    NA
7      2     2    NA
8      2     3     6
9      2     4    NA
10     2     5    NA
11     2     6     5
12     2     8    NA
13     3     2     3
14     3     3    NA
15     3     4    NA
16     3     5     8
17     3     6    NA
18     3     8    10