Given an nxm matrix A I want to compute the nxm matrix B whose ij-th
element is the sum of the elements of A lying on the diagonal that ends
with element ij, i.e.,
b_ij = a_ij + a_(i-1)(j-1) + a_(i-2)(j-2) + ...
In APL (which I no longer use), I would use the 'rotate' operator to
derive
an array whose columns are diagonals of the given array and then cumulate
down columns. Is there a similar operator in R, or is there another/better way?
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you could index the elements explicitly via index.matrix <- matrix(seq(to=i,len=min(i,j)),seq(to=j,len=min(i,j)),ncol=2) and so b_ij = sum(a.matrix[index.matrix]), or you could use the function diag on the appropriate sub matrices of a.matrix. Alec Stephenson tel +44 (0) 1524 593950 Department of Mathematics and Statistics fax +44 (0) 1524 592681 Lancaster University email a.stephenson at lancaster.ac.uk Lancaster LA1 4YF On Sat, 19 May 2001, Griffith Feeney wrote:> Given an nxm matrix A I want to compute the nxm matrix B whose ij-th > element is the sum of the elements of A lying on the diagonal that ends > with element ij, i.e., > > b_ij = a_ij + a_(i-1)(j-1) + a_(i-2)(j-2) + ... > > In APL (which I no longer use), I would use the 'rotate' operator to derive > an array whose columns are diagonals of the given array and then cumulate > down columns. Is there a similar operator in R, or is there another/better way? > > -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- > r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html > Send "info", "help", or "[un]subscribe" > (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch > _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
----- Original Message ----- From: "Griffith Feeney" <gfeeney at gfeeney.com>> Given an nxm matrix A I want to compute the nxm matrix B whose ij-th > element is the sum of the elements of A lying on the diagonal that ends > with element ij, i.e., >How about sum( diag( A )[ 1:i ] )?> b_ij = a_ij + a_(i-1)(j-1) + a_(i-2)(j-2) + ... > > In APL (which I no longer use), I would use the 'rotate' operator toderive> an array whose columns are diagonals of the given array and then cumulate > down columns. Is there a similar operator in R, or is there another/betterway?> > -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-> r-help mailing list -- Readhttp://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html> Send "info", "help", or "[un]subscribe" > (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch >_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._. _._>-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._