Selecting timepoints in longitudinal data

[Stanley3]

Hi,

I have a dataset with multiple timepoint measurements for the same ID. For each unique ID, I need to keep only the earliest observation and delete the rest. How can I code this?

Additionally, using the example below, how can I fill in the missing value for the 'sex' variable at timepoint 1 with the value from timepoint 2?

Thank you!

ID	Timepoint	Sex
0001	1
0001	2	Female
0001	3	Female
0002	2	Male
0002	3	Male
0003	2	Male
0003	4	Male

[PaigeMiller · Accepted solution]

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@Stanley3 wrote:

I have a dataset with multiple timepoint measurements for the same ID. For each unique ID, I need to keep only the earliest observation and delete the rest. How can I code this?

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data want;
    set have;
    by id;
    if first.id;
run;

Additionally, using the example below, how can I fill in the missing value for the 'sex' variable at timepoint 1 with the value from timepoint 2?

See Look Ahead and Look Back

[Stanley3]

Brilliant, thank you so much!