[R] using sapply to apply function to some columns of a dataframe

Hello: I would like to sum every x columns of a dataframe for each row. For instance, if x is 10, then for dataframe df, this function will sum the first ten elements together and then the next ten: sapply(list(colnames(df)[1:10], colnames(df)[11:20]),function(x)apply( df[,x], 1, sum)) If the

[R] using chron() to convert julian -> calendar dates but ignoring leap years

Hello: I am using R 2.7.2 for Windows. I have been using chron() to convert from Julian to calendar dates. How do I ignore leap years? Thanks. Cheers, Michael -- Michael I. Westphal, PhD Africa Region Water Resource