Tranfroming a sting date variable into a yearly time variable in order to draw a time-graph

[Aziz Essouaied]

Hello Stata people;

This is my data:

* Example generated by -dataex-. To install: ssc install dataex
clear
input str10 date str16 typeuinite byte nombreunite
"2008-12-31" "lait et derivés"  10
"2008-12-31" "unité de sechage"  1
"2008-12-31" "unité de fromage" 25
"2008-12-31" "unité de yaourte"  7
"2009-12-31" "lait et derivés"  10
"2009-12-31" "unité de sechage"  1
"2009-12-31" "unité de fromage" 25
"2009-12-31" "unité de yaourte"  7
"2010-12-31" "lait et derivés"  10
"2010-12-31" "unité de sechage"  1
"2010-12-31" "unité de fromage" 25
"2010-12-31" "unité de yaourte"  7
"2011-12-31" "lait et derivés"  10
"2011-12-31" "unité de sechage"  1
"2011-12-31" "unité de fromage" 25
"2011-12-31" "unité de yaourte"  7
"2012-12-31" "lait et derivés"  10
"2012-12-31" "unité de sechage"  1
"2012-12-31" "unité de fromage" 25
"2012-12-31" "unité de yaourte"  7
"2013-12-31" "lait et derivés"   7
"2013-12-31" "unité de sechage"  1
"2013-12-31" "unité de fromage" 40
"2013-12-31" "unité de yaourte"  4
"2014-12-31" "lait et derivés"   9
"2014-12-31" "unité de sechage"  1
"2014-12-31" "unité de fromage" 26
"2014-12-31" "unité de yaourte"  7
"2015-12-31" "lait et derivés"  10
"2015-12-31" "unité de sechage"  1
"2015-12-31" "unité de fromage" 40
"2015-12-31" "unité de yaourte"  4
"2016-12-31" "lait et derivés"  10
"2016-12-31" "unité de sechage"  1
"2016-12-31" "unité de fromage" 40
"2016-12-31" "unité de yaourte"  4
"2017-12-31" "lait et derivés"  11
"2017-12-31" "unité de sechage"  2
"2017-12-31" "unité de fromage" 25
"2017-12-31" "unité de yaourte"  9
"2018-12-31" "lait et derivés"  11
"2018-12-31" "unité de sechage"  2
"2018-12-31" "unité de fromage" 25
"2018-12-31" "unité de yaourte"  9
"2019-12-31" "lait et derivés"  11
"2019-12-31" "unité de sechage"  2
"2019-12-31" "unité de fromage" 25
"2019-12-31" "unité de yaourte"  9
"2020-12-31" "lait et derivés"  11
"2020-12-31" "unité de sechage"  2
"2020-12-31" "unité de fromage" 25
"2020-12-31" "unité de yaourte"  9
"2021-12-31" "lait et derivés"  11
"2021-12-31" "unité de sechage"  2
"2021-12-31" "unité de fromage" 25
"2021-12-31" "unité de yaourte"  9
end

As you can see, I have a problem with the date variable, as it is in string format, I can't transform it into a tsset date variable. Is there a way to do that? Moreover, I just wanna keep just the year, as the months and the days are repetetive and the same, so they won't offer me any plus for my analysis.
The category variable is types of units, and then the third variable is the number of each unit type.

Could I get some help dealing with the date variable please? Thanks!

[Nick Cox]

String is a set of variable or storage types, which is the issue here, not (display) format.

gen year = real(substr(date, 1, 4))

should work fine here. Extract the first 4 characters and then push through the real() function.