What you need to realize is that R does vectorized computation in `Fortran' order. Here's a perhaps more illuminating example:
> tr <- rep(1:2, 3) > tr [1] 1 2 1 2 1 2 > ex1 <- as.data.frame(matrix(1:12, 2, 6)) > ex1 V1 V2 V3 V4 V5 V6 1 1 3 5 7 9 11 2 2 4 6 8 10 12 > tr * ex1[1,] V1 V2 V3 V4 V5 V6 1 1 6 5 14 9 22 > (tr * ex1)[1,] V1 V2 V3 V4 V5 V6 1 1 3 5 7 9 11 When you do (tr * ex1)[1,], R multiplies tr and ex1 element-by-element, stacking _columns_ of ex1 to match tr, and recyle the elements of tr to match the length of the `stacked' ex1. Andy > From: Wayne Jones > > Hi there fellow R-users, > > Im seeing some strange behaviour when I multiply a vector by a matrix > > Here is my script: > > > tr > 1 2 3 4 5 6 > 0.2217903 0.1560525 0.1487908 0.1671354 0.1590643 0.1471667 > > > > ex1 > a b c d e f > 1 0.2309579 -3.279045 -0.6694697 -1.1024404 0.2303928 -1.5527404 > 2 -0.2865357 -2.519789 -0.1138712 -0.3571832 -2.6727913 -0.3296945 > > > is.vector(tr) > [1] TRUE > > > is.data.frame(ex1) > [1] TRUE > > > tr* ex1[1,] > a b c d e f > 1 0.05122423 -0.5117031 -0.09961092 -0.1842569 0.03664727 -0.2285117 > > > (tr* ex1)[1,] > a b c d e f > 1 0.05122423 -0.4878917 -0.1064887 -0.2445106 0.03428033 -0.2469855 > > > Notice that the output from tr * ex[1,] is different from > (tr* ex1)[1,] > Especially element number 4. > > I would naturally expect both vectors to be equivalent. > > > Can anyone shed any light on my predicament?? > > > > > version > _ > platform i386-pc-mingw32 > arch i386 > os mingw32 > system i386, mingw32 > status > major 1 > minor 9.1 > year 2004 > month 06 > day 21 > language R > > > > Regards > > Wayne Jones > > > > > > > KSS Ltd > Seventh Floor St James's Buildings 79 Oxford Street > Manchester M1 6SS England > Company Registration Number 2800886 > Tel: +44 (0) 161 228 0040 Fax: +44 (0) 161 236 6305 > mailto:[EMAIL PROTECTED] http://www.kssg.com > > > The information in this Internet email is confidential and > m...{{dropped}} > > ______________________________________________ > [EMAIL PROTECTED] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html > > ______________________________________________ [EMAIL PROTECTED] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
