st: Create a new variable based on the current observation and values of other observations in the same group

[Huanhuan Shi <huanhuanshi09@gmail.com>]

Dear Statalist,

I have a problem which is similar to but different from this post.
http://www.stata.com/support/faqs/data-management/creating-variables-recording-properties/

I tried to modify the code suggested by Nicholas J. Cox but can not
figure it out. Hope I can get help from you.
The problem I am facing is as follows:

First, the data structure is shown below. I have family groups and
individuals in each family group.

        family    person   sex      age
  1.         1          1          1         36
  2.         1          2          1         16
  3.         1          3          1         14

  4.         2          1          0         45
  5.         2          2          1         42
  6.         2          3          0         14
  7.         2          4          1         12
  8.         2          5          0         10

  9.         3          1          0         39
10.         3          2          1         36
11.         3          3          0         11
12.         3          4          1          9
13.         3          5          1          7
14.         3          6          1          3


What I want to do is to create a new variable "count" that count the
number of individual that sex is 1  and10 years younger than the
person within the same family. So the result should be like:


        family    person   sex      age      count
  1.         1          1          1         36           2
  2.         1          2          1         16           0
  3.         1          3          1         14           0

  4.         2          1          0         45           1
  5.         2          2          1         42           1
  6.         2          3          0         14           0
  7.         2          4          1         12           0
  8.         2          5          0         10           0

  9.         3          1          0         39           3
10.         3          2          1         36           3
11.         3          3          0         11           0
12.         3          4          1          9            0
13.         3          5          1          7            0
14.         3          6          1          3            0


Thank you so much!!

Huanhuan
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