R help - Mar 2010 - Preserving both yearmon and numeric data in an xls object

Hi R gourmets,

I am trying to convert an HTML table into an xts object. The table has 
six columns, with the data of interest in a single row with each cell 
containing a long, \n-delimited character string. Initially, I work with 
these strings as elements in a list. This is necessary because the 
strings in each cell do not translate into a regular matrix with 
equal-length columns. Once I fix the entries, I'm ready to convert them 
into an xts object. The first two columns of the original table contain 
dates, and I want them to be of type "yearmon" in the xts object. The 
other four columns have numeric data.

Here's my problem. If I convert the list into a data frame on the way to 
making it an xlt, the first two columns correctly keep the data as the 
yearmon class, but the remaining columns are converted to character 
class. Alternatively, if I convert the list into a matrix on the way to 
making the xlt, all six columns become numeric; the first two columns 
lose their yearmon class.

How can I make an xlt from a list, such that the first two columns are 
yearmon and the last four are numeric?

Thanks.

     Marsh Feldman

P.S. Here is some sample code:

     > #... input has been converted to a list of length 6; each element
    is a vector, but they themselves are of different length
     > #... fix the 6 vectors to have equal length
     > mylist[1:2] <- lapply(mylist[1:2], as.yearmon)        # Convert
    the first two elements into yearmon class
     > #... Now try one of the following; tindex is the time index in
    yearmon format
     > myxts <- as.xts(as.data.frame(mylist), order.by=tindex)    # this
    makes columns 3-6 of myxts all have class = character
     > myxts <- as.xts(matrix(unlist(mylist), ncol=6), order.by=tindex)
    # this makes myxts entirely numeric
             I even tried using the following statement afterwards but
    had no luck
     > myxts[,1] <- as.yearmon(myxts[,1])



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