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

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

Subject |
RE: st: extract rowname corresponding to row index of matrix |

Date |
Thu, 2 Apr 2009 12:32:27 +0100 |

I think Ben slightly understates how easy it is -- once you know the syntax, naturally. . mat A = (1, 1 \ 2, 2) . mat rownames A = one two Here are two further variations on how to do it. One nests function calls: . di "`: word 2 of `: rownames A''" two The other uses -tokenize- first: . tokenize "`: rownames A'" . di "`2'" two Nick n.j.cox@durham.ac.uk Ben Jann The trick is as follows: <---> matrix input BETA=( 193\ 30 \ 133 \ 51\ 9.8 \ 0.1 ) matrix rownames BETA= dog cat rat mouse flea bubonic matrix colnames BETA=IQ mat lis BETA local r = rownumb(matrix(BETA),"bubonic") local c = colnumb(matrix(BETA),"IQ") matrix RowNamesNoLongerLost=BETA[`r',1...] matrix RowNamesNoLongerLost=RowNamesNoLongerLost[1...,`c'] mat lis RowNamesNoLongerLost <---> However, if you just want to extract the names (and if you know that the names do not contain blanks!) you can also simply type: <---> local colnms: coln BETA local rownms: rown BETA local colname: word 1 of `colnms' local rowname: word 6 of `rownms' <---> On Thu, Apr 2, 2009 at 12:57 AM, Jacob Wegelin <jacob.wegelin@gmail.com> wrote: > Suppose we have a matrix BETA with -rownames- and -colnames-. > > Given the names of a row and of a column in BETA, it is possible to > extract the indices of that row and of that column, as shown below. > > But is there an equally simple approach to the reverse problem? I > mean: Given a row index, is there an elegant way to extract the name > of that row? > > The solution below seems clumsy. As seen with -matrix LostRowNames-, > extracting a one-row matrix from a one-column matrix causes the > -rownames- to be lost. Thus my program uses a column join, which seems > like a kludge. > > /* BEGIN STATA CODE */ > > clear all > matrix input BETA=( 193\ 30 \ 133 \ 51\ 9.8 \ 0.1 ) > matrix rownames BETA= dog cat rat mouse flea bubonic > matrix colnames BETA=IQ > mat lis BETA > > di "index of row called bubonic is " rownumb(matrix(BETA),"bubonic") > di "index of column called IQ is " colnumb(matrix(BETA),"IQ") > > matrix LostRowNames=BETA[1,1] > mat lis LostRowNames > > capture program drop getRowName > program define getRowName, rclass > local thismatrix="`1'" > local rowindex=`2' > matrix TWO= `thismatrix', `thismatrix' > matrix TEMPORARY=TWO[`rowindex',1..2] > local rowname: rownames TEMPORARY > return local matrixname="`thismatrix'" > return scalar rowindex=`rowindex' > return local rowname = "`rowname'" > end > > getRowName BETA 1 > return list > getRowName BETA 5 > return list > > /* END STATA CODE */ > * * 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: extract rowname corresponding to row index of matrix***From:*Jacob Wegelin <jacob.wegelin@gmail.com>

**Re: st: extract rowname corresponding to row index of matrix***From:*Ben Jann <ben.jann@gmail.com>

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