Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

From |
jo la frite <jo_la_frite@yahoo.com> |

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

Subject |
Re: st: Comparing strings |

Date |
Mon, 26 Mar 2012 09:34:27 -0700 (PDT) |

dear Nick, Thanks for your reply and sorry for being too cryptic with my question. I am trying to merge 2 datasets, in which observations (firms) are identified by their names. The names do not match exactly in the 2 datasets so I am doing a "fuzzy match". My idea is to match 2 names if a large enough fraction of a name from dataset 1 (say name1) is in a name from dataset 2 (name 2). For example, "abcde" could be matched with "abcdtyuk" because the FIRST 4 letters are in common out of an average of (5+8)/2=6.5. It is important that the comparison sticks to the ordering of the letters. So "abcde" is not matched with "edcba" or "bacde", even though the letters are the same but in a different order. Does that make any sense? thanks again for your help. Jo ________________________________ From: Nick Cox <njcoxstata@gmail.com> To: statalist@hsphsun2.harvard.edu Sent: Monday, March 26, 2012 11:30 AM Subject: Re: st: Comparing strings This is a bit better: mata : string scalar strscalarsort(string scalar mystring) { real scalar len, i string colvector work len = strlen(mystring) work = J(len, 1, "") for(i = 1; i <= len; i++) work[i] = substr(mystring, i, 1) _sort(work, 1) return(invtokens(work', "")) } end I still don't know what the real problem is, so I am just playing. But if you wanted to compare strings regardless of order of characters something like this would seem needed as a first step. On Mon, Mar 26, 2012 at 1:51 AM, Nick Cox <njcoxstata@gmail.com> wrote: > -indexnot()- is a function, not a command. > > It's not clear to me what you want, but you can check for whether the > same letters occur in two strings, at the cost of some programming. > For example, a Mata function can be written to sort the characters of > a string scalar into alphabetical order. Here is one: > > mata : > > string scalar deorst(string scalar mystring) { > > real scalar len > string vector work > len = strlen(mystring) > work = J(len, 1, "") > for(i = 1; i <= len; i++) work[i] = substr(mystring, i, 1) > _sort(work, 1) > mystring = "" > for(i = 1; i <= len; i++) mystring = mystring + work[i] > return(mystring) > } > > end > > . mata : deorst("sorted") > deorst > > . mata : deorst("backwards") > aabcdkrsw > > On Sun, Mar 25, 2012 at 10:20 PM, jo la frite <jo_la_frite@yahoo.com> wrote: >> thanks Nick and Eric. As far as I understand, the indexnot command compares strings regardless of the ordering of the characters in the string. for example, "frog" and "ogfr" are viewed as identical by indexnot. >> >> >> Is there a way of controling for the ordering of the characters. So for example, "comparing "frog" and "fragro" retuns 3 (position of the first character from "frog" not in "fragro"). > > From: Nick Cox <njcoxstata@gmail.com> > >> Stata naturally does have a concept of alphanumeric order for strings; >> otherwise it could not -sort- them. Consider >> >> . di ("frog" < "toad") >> 1 >> >> . di ("frog" < "foo") >> 0 >> >> The first statement is true and the second false. Otherwise put, with >> strings < means "precedes" and > means "follows" in alphanumeric >> order. >> >> This allows one step further forwards: >> >> gen compare = cond(str1 > str2, indexnot(str1, str2), -indexnot(str1, str2)) >> >> If strings are identical, this yields 0. Jo did not make explicit that >> this is what SAS does too, but either way it seems logical to me. >> >> Nick >> >> On Sat, Mar 24, 2012 at 10:47 PM, Eric Booth <eric.a.booth@gmail.com> wrote: >> >>> Take a look at the string function (-help string_functions-) indexnot() (e.g., "gen x = indexnot(string1, string2)" ) which will give you the leftmost position where the two strings differ. >>> This Stata string function does not assign the positive/negative sign like the sas function you describe, but you can code those yourself by using other string functions to find how they differ in order/sequence/length. >> >> On Mar 24, 2012, at 5:12 PM, jo la frite wrote: >> >>>> Is there a Stata function that correspondons to the Sas function "COMPARE". It allows to compare strings. Specifically, in Sas COMPARE(string-1, string-2) returns a numeric value. The sign of the result is negative if string-1 precedes string-2 in a sort sequence, and positive if string-1 follows string-2 in a sort sequence. The magnitude of the result is equal to the position of the leftmost character at which the strings differ. * * 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/ ; * * 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/

**Follow-Ups**:**Re: st: Comparing strings***From:*Eric Booth <eric.a.booth@gmail.com>

**References**:**st: Comparing strings***From:*jo la frite <jo_la_frite@yahoo.com>

**Re: st: Comparing strings***From:*Eric Booth <eric.a.booth@gmail.com>

**Re: st: Comparing strings***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: Comparing strings***From:*jo la frite <jo_la_frite@yahoo.com>

**Re: st: Comparing strings***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: Comparing strings***From:*Nick Cox <njcoxstata@gmail.com>

- Prev by Date:
**Re: st: Difference between xtreg and reg for Pooled OLS?** - Next by Date:
**Re: st: Comparing strings** - Previous by thread:
**Re: st: Comparing strings** - Next by thread:
**Re: st: Comparing strings** - Index(es):