I have a more challenging question for the group: I've been honing some of my beginning J skills using downloaded stock market data (DJIA) as a convenient "real" (and of practical interest) array to practice with (of course, AFTER "getting it right" with small sample arrays!). The data I have is daily from 1928 (getting prior data someday soon), varying anywhere from, theoretically, 1 to 6 trading days per week. I'd like to derive some weekly figures from the daily data, but the variability of the trading week is a "fly in the ointment", so one can't just take every so many days of data. Slightly redefined, the trading week is all trading days between Sundays, which are easy to calculate. However, another "fly in the ointment" is that Sunday dates are not included in the downloaded market data, seemingly excluding the use of any kind of "cut" operation on the sequence of data in the array.
Is there any way to use a "Sunday" formula to pass against Monday-through-Saturday data in an array (Yahoo data consists of date, open, high, low, close, volume, adjusted close; I'd probably be using the first and last columns here), so that some processing (via another function) could be performed on whatever data exists BETWEEN the Sundays? Or does one have to insert all the Sunday dates (with perhaps zero data values) into the array, using perhaps J (or some other language) and then attempt to do a "cut" operation using the added info? Or is there some other approach? I've been giving a lot of thought for the past week or so to this problem, but my meager knowledge at this point seems not yet enough to solve the problem. Thanks in advance for any insights you can share! Harvey ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
