st: How to fill in the missing data

[Ching Wong <ching.y.wong@student.adelaide.edu.au>]

Hi,

I have a dataset as following:

id age weight
1   21   50.2
1   22
1   23   52.9
1   24   51.0
1   25
2   22
2   23
2   25   60.2
3   21

And I would like to create a new variable "weight2" and fill in the
missing data based on the previous value

My expected output value should be as follows:

id age weight weight2
1   21   50.2     50.2
1   22       .       50.2
1   23   52.9     52.9
1   24   51.0     51.0
1   25      .        51.0
2   22      .            .
2   23      .            .
2   25   60.2     60.2
3   21      .            .

I have tried the command below but that cannot produce what I expected.

- bysort id (age): gen weight_hat = weight[_n-1]

It is very obvious that command is missing something. So what will be
the correct command in this case?

Cheers,

Wong
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