On 27-Aug-10 17:17:50, Marcus Drescher wrote: > Hi all, > I want to calculate in each row a ratio based on number in the current > row and the previous row. > Is there a way to do this without for-loops because that is extremely > slow. > > A B > [1] 2 2 > [2] 2 3 > [3] 4 5,5 > ... > > B2 = A2 + 0.5*B1 > > Thanks in advance. > Best > Marcus
If n is the total number of rows, then : B[(2:n)] <- A[(2:n)] + 0.5*B[1:(n-1)] should work! This assumes that A and B have been extracted as vectors, or can be referred to separately as in a dataframe (say D), like D$B[(2:n)] <- D$A[(2:n)] + 0.5*D$B[1:(n-1)] Ted. -------------------------------------------------------------------- E-Mail: (Ted Harding) <ted.hard...@manchester.ac.uk> Fax-to-email: +44 (0)870 094 0861 Date: 27-Aug-10 Time: 18:34:27 ------------------------------ XFMail ------------------------------ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
