Create variable difference from date

[Joan Marti]

Hi,


I have a dataset with a weekly date variable and my explanatory variable X. The treatment in my dataset happens on the week of the 14/01/2010.

I want to create a variable "difference" as shown below, which measures weeks from treatment.

date	x variable	difference
01/01/2010	5.0	-2
07/01/2010	4.3	-1
14/01/2010	2.6	0
21/01/2010	6.0	1
28/01/2010	9..8	2

What is the best way to do this? I have tried a few manual ways but they seem to take very long and are extremely inefficient.

Thank you very much in advance!

[Nick Cox]

Please use dataex. (FAQ Advice #12). This data example is based on copy and paste from #1 and some engineering. You didn't mean what you typed for the xvariable, but that doesn't affect the question.

* Example generated by -dataex-. For more info, type help dataex
clear
input str4 xvariable byte difference float date
"5.0"  -2 18263
"4.3"  -1 18269
"2.6"   0 18276
"6.0"   1 18283
"9..8"  2 18290
end
format %td date

. gen wanted = (date - mdy(1, 14, 2010)) / 7

. l

     +---------------------------------------------+
     | xvaria~e   differ~e        date      wanted |
     |---------------------------------------------|
  1. |      5.0         -2   01jan2010   -1.857143 |
  2. |      4.3         -1   07jan2010          -1 |
  3. |      2.6          0   14jan2010           0 |
  4. |      6.0          1   21jan2010           1 |
  5. |     9..8          2   28jan2010           2 |
     +---------------------------------------------+

. gen wanted2 = round(wanted, 1)

. l

     +-------------------------------------------------------+
     | xvaria~e   differ~e        date      wanted   wanted2 |
     |-------------------------------------------------------|
  1. |      5.0         -2   01jan2010   -1.857143        -2 |
  2. |      4.3         -1   07jan2010          -1        -1 |
  3. |      2.6          0   14jan2010           0         0 |
  4. |      6.0          1   21jan2010           1         1 |
  5. |     9..8          2   28jan2010           2         2 |
     +-------------------------------------------------------+

The irregular spacing of dates in the data example raises a serious question about what exactly you want.

[Joan Marti]

Thank you, this worked!