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From |
Matthew White <mwhite@poverty-action.org> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Copying structures |

Date |
Mon, 15 Apr 2013 00:26:04 -0400 |

Hi Statalist members, I'm using a Mata structure in a function that looks like this: void function write_lists(struct odklist rowvector lists) { real scalar i struct odklist scalar list struct odklist rowvector newlists newlists = odklist() for (i = 1; i <= length(lists); i++) { list = lists[i] // Modify variable list. // If list satisfies certain criteria, add it to newlists. } // More code for (i = 1; i <= length(newlists); i++) { // Do stuff with newlists[i]. } } My problem is that over the course of the function, the argument lists is modified: after each element of lists is copied to list (-list = lists[i]-), the element is modified whenever list is modified. It's as if list and lists[i] have been linked. Here's a simpler example: mata: struct point { real scalar x, y } void function myfunc() { struct point rowvector mypoints mypoints = point(2) mypoints[1].x = mypoints[1].y = 1 mypoints[2].x = mypoints[2].y = 2 liststruct(mypoints) mysubroutine(mypoints) liststruct(mypoints) } void function mysubroutine(struct point rowvector mypoints) { struct point scalar firstpoint firstpoint = mypoints[1] firstpoint.x = firstpoint.x + 1 } myfunc() end Before -mysubroutine()-, mypoints[1].x = 1. Afterwards, mypoints[1].x = 2. This is despite the fact that the only use of mypoints is to make firstpoint a copy of mypoints[1]. It seems to work fine to copy a struct scalar to another struct scalar or a struct vector to another struct vector, but copying an element of a struct vector to a struct scalar results in this behavior. I'm using Stata 12.1 SE on Windows 7. Any suggestions would be much appreciated. Thanks, Matt -- Matthew White Senior Project Associate Innovations for Poverty Action 101 Whitney Avenue, New Haven, CT 06510 USA www.poverty-action.org * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Copying structures***From:*Matthew Baker <matthew.baker@hunter.cuny.edu>

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