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From |
Martin Hällsten <martin.hallsten@sofi.su.se> |

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

Subject |
st: RE: distance calculation and reshape |

Date |
Fri, 19 Oct 2007 13:15:33 +0200 |

Hi, I have a problem with the reshape command which seems extremely slow. My data file contains x and y coordinates for n different points, and I want to calculate the distance between each point (using pythagora’s theorem). For various reasons, I want to calculate n*n distances rather than (n*(n-1))/2 unique distances. The following loop simulates exactly the kind of data I have and then calculates the problem (n points is here set to 10). // SIMULATION local n = 10 range point 1 `n' `n' gen x = int(abs(uniform()*10000000)) gen y = int(abs(uniform()*10000000)) // CALCULATION local rows = _N forvalues n1 = 1/`rows' { gen point_`n1' = point[`n1'] gen x_`n1' = x[`n1'] gen y_`n1' = y[`n1'] } reshape long point_ x_ y_ , i(point) j(row) gen xdiff = abs(x-x_) gen ydiff = abs(y-y_) gen distance = sqrt((xdiff^2)+(ydiff^2)) The problem is that I need to do this for 9230 points. Everything goes fine (and fast) until the reshape command. Then Stata seem to get stuck. The thing is that I run this on a multiprocessor Windows Vista machine using StataMP 9.2. I have set the memory to 25 GB which is more than sufficient. I have also set the number of maximum variables to 32000. So it shouldn’t really be the machinery that fails. I had the above loop with n = 9230 running for three days (72 hours!), but the reshape command couldn’t complete within that time. Does anyone have suggestions how the calculation could be run faster/without using the reshape command? And why is reshape so tediously slow? Thanks Martin Hällsten martin.hallsten@sofi.su.se * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: RE: distance calculation and reshape***From:*"Austin Nichols" <austinnichols@gmail.com>

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