R: using ddply in a loop over data frame columns

Question

I need to calculate and add to a data frame multiple new columns based on the values in each column in a subset of columns in the data frame. These columns all hold time series

Answer 1

In your loop, since myxts is not part of the data frame, it is not split up in the ddply statement along with everything else. Change it to:

mydf$myxts <- xts(mydf[, newcolnames[i]], order.by = mydf$mydate)

I don't know of any way to use dynamically generated names with transform.