JasperReports CategoryDataset has less data than expected? - graph

Question

I'm trying to develop a ChartCustomizer that takes the data from a chart and converts it into a histogram (because JR does not directly support histograms). It's a fairly simple implementation with hard-coded intervals, etc. mostly as a proof-of-concept at this point.
The data I'm analyzing is HTTP response-time data of the form [date, response-time] and I have a CSV file with 18512 records in it. In my summary band, I have 3 items:
A text field dumping $V{REPORT_COUNT} (it reports 18512 in iReport's report preview)
A time series showing all the data points [date, response-time]
A category plot containing all the data points in a single series [category=$F{DATE}, value=$F{RESPONSE_TIME}]
I decided that the most straightforward way to build a histogram would be to use the Category plot because it had the right structure for the final histogram chart.
When the ChartCustomizer runs, it dumps out all kinds of good information about the data set, including the size. Strangely, the size is 10252: it's missing something like 8000 data points. I can't understand why the category plot would have fewer data points than the whole data set.
Any ideas?

Answer 1

Answering my own question in case others run across this foolish user error.
The problem was that CategoryDataset only allows one data point per "category", and in my case, "category" was a java.util.Date captured from the web server log. Apparently, nearly half of my dates were duplicates and so part of the data set overwrote the other half, leaving a subset of the data.
That should have been totally obvious to me at the outset, because that is exactly how a category dataset works.
Anyhow, simply changing the category plot series's "category expression" from $F{DATE} to $V{REPORT_COUNT} gave each datum a unique category which makes everything work.