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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: generate new variable from differencing where subtracted variable is fixed |

Date |
Fri, 5 Mar 2010 16:29:20 -0000 |

The solution is simpler. bysort year : gen diff = x1 - x2[1] Why is your code not working? Think it through step by step: _n == 1 is true (1) when _n is 1 and false otherwise (0). So x2[_n==1] is x2[1] or x2[0] as the case may be. But x2[0] is not part of your data, and Stata can only substitute missing when it evaluates it. So -diff- is only non-missing in the first observation in each -year-, as you report. However, your solution needs care when extending to panels, Nick n.j.cox@durham.ac.uk Johannes Schoder I try to calculate the difference between two variables for a panel data set, where the subtracted variable (here x2) is always the first observation of each year: For example: Year x1 x2 difference: x1-x2 if x2 is the first obs. of the year 1960 5 8 5-8 1960 4 10 4-8 1960 2 3 2-8 1961 5 7 5-7 1961 1 2 1-7 1961 3 5 3-7 I tried something like: bysort year: gen difference= x1-x2[_n==1] but Stata does only calculate the first observation for each year and otherwise generates missings. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: generate new variable from differencing where subtracted variable is fixed***From:*Johannes Schoder <johannes.schoder@soi.uzh.ch>

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