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From |
"Sarah Edgington" <sedging@ucla.edu> |

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

Subject |
st: RE: Problems with execution of conditional branching.. |

Date |
Wed, 13 Mar 2013 18:22:26 -0700 |

I think Scott's suggestion about how to tackle this problem probably offers a more efficient strategy than this one. However, know why this example doesn't work will probably also be helpful to you in the future. The problem is that the if statements here are only evaluating your first observation. See -help ifcmd- and -help if- for more details. The thing that I think isn't entirely clear from the helpfile is that the programming if checks the conditional statement once and if it's true it takes the action in the braces. Unless otherwise specified it evaluates the first observation in the data when the conditional involves a variable. To get an observation by observation evaluation of a conditional you have to use the if expression after a command. So -gen event_month=substr(opendate,6,1) if comma_3==2 & comma_2==1- will check that condition for each observation and create the relevant variable. Contrast that with a simplification of your first conditional (written as a single line instead of in braces) -if comma_3==2 & comma_2==1 gen event_month = substr(opendate, 6,1)- Here Stata is only evaluating the conditional once. Since it involves variables (which, by virtue of being variables are going to be different across observations) there has to be some rule about what observation is used to evaluate this statement. Since you haven't specified an observation number to evaluate, it defaults to the first observation. So running your code will perform only one of the four possible sets of commands you specified. Which one it performs depends entirely on the first observation in the data. Hopefully that helps clear up what's going on here. -Sarah -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Mani Subramani Sent: Wednesday, March 13, 2013 3:39 PM To: statalist@hsphsun2.harvard.edu Subject: st: Problems with execution of conditional branching.. I am new to Stata but I have programmed before (SPSS, SAS) etc. andI am confused by the behavior of STATA in executing the code below. I am trying to parse a date-string that is currently in one variable with format "yyyy-mm-dd-hh-ss"..it unfortunately has 1 digit months and days. Further, because of the unconventional numbering of months (0-11, rather than 1-12), I am unable to use the much easier dofc(Opendate)) command build into STATA that does some intelligent validation and fails to import dates like October 31 (which is indicated in my data as 2012,9,31 I use the location of the comma separators to parse the string with strpos to create variables...the code runs..but it clearly does not work properly. I still have some dates with ",7" which I find inexplicable because the branch where this should get executed picks only 1 character dates. I have four mutually exclusive branches to handle the different combinations of 2 digit and 1 digit month, day...but for some reason..this is not working properly. Some of the statements within branches that are excluded by the if seem to be getting executed... This would be ideally executed with a Case statement -or with Regex (I tried but couldnt figure it out) but the code below should be doing that but it clearly isn't. Thanks in advance for your help thanks in advance for your help Mani ==================== gen event_year = substr(opendate, 1,4) //this works just fine, year always 4 digits // I test for pattern of month, day based on location of comma3 and comma2 in date string //date string format: yyyy,mm,dd - month, day can be either 1 or 2 digits // location of third comma - it is either in 9, 10 or 11 gen comma_3 = strpos(substr(opendate,9,3), ",") // 1= 1 dig month& date, 3+2 dig month, date, 2 = unclear gen comma_2 = strpos(substr(opendate,7,2), ",") //when comma3 is ; comma_2==1 indicates m,dd; comma_2==2 - mm,d if comma_3==2 & comma_2==1 { gen event_month = substr(opendate, 6,1) gen event_day = substr(opendate, 8,2) } else if comma_3==2 & comma_2==2 { gen event_month = substr(opendate, 6,2) gen event_day = substr(opendate, 9,1) } else if comma_3==1 { gen event_month = substr(opendate, 6,1) gen event_day = substr(opendate, 8,1) } else if comma_3==3 { gen event_month = substr(opendate, 6,2) gen event_day = substr(opendate, 9,2) } ================== results=== opendate comma_3 comma_2 event_year event_month event_day 2012,9,18,13,21,12 2 1 2012 9 18 2012,9,18,10,51,33 2 1 2012 9 18 2012,9,22,16,23,48 2 1 2012 9 22 2012,10,29,14,59,52 3 2 2012 1 ,2 2012,10,21,23,57,29 3 2 2012 1 ,2 2012,10,22,20,10,23 3 2 2012 1 ,2 * * 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/ * * 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: RE: Problems with execution of conditional branching..***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: RE: Problems with execution of conditional branching..***From:*Mani Subramani <subra010@umn.edu>

**References**:**st: Problems with execution of conditional branching..***From:*Mani Subramani <subra010@umn.edu>

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