Dynamically Charting with Variable Dates and Data

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I'm generating charts and I'm letting the user specify the date range. The problem is that there might be anywhere from 5-1000 data points and the values might be from 0 to 1,000,000.

I'm primarily using Open Flash Charts2 and Google Charts API.

I need to generate the Y axis step value and X step value and X labels. I think the most X labels I can fit really is about 30. So for a 30 day range that's really easy. Just show every label. But if they have 500 data points what do I do? 5000 / 30 = 166 x step value? Same with Y step value?

Does every single person that comes across this kind of charting problem just re-invent the wheel, or are there good libraries for this stuff, or is there some simple formulas for making this trivial to do manually?

Thanks in advance.

Comment on Dynamically Charting with Variable Dates and Data

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Re: Dynamically Charting with Variable Dates and Data by moritz (Cardinal) on Jan 12, 2009 at 08:36 UTC
I didn't like GD::Graph's algorithm to determine the maximal value, so I invented my own: `use POSIX qw(log10); my $round_to = 10 ** int(log10 $max) / 5; $max = $round_to * (1 + int($max / $round_to)); $p->set(y_max_value => $max );` [download] In this case $max is the maximum value that appears in the data set. $round_to is first set to the next lower power of ten (so for example 35 is set to 10) and then divided by 5 (so that would be 2 here). Then the maximum value is set to the next higher step of $round_to. You can simply use $round_to, or a multiple thereof, as step value, or be inspired by my usage of logarithm+exponentiation+rounding to find your own formula.	[reply] [d/l]
Re^2: Dynamically Charting with Variable Dates and Data by Anonymous Monk on Jan 12, 2009 at 22:57 UTC
I like the numbers your algorithm is giving me. I'm going to use it. Thanks.	[reply]
Re: Dynamically Charting with Variable Dates and Data by Anonymous Monk on Jan 12, 2009 at 22:23 UTC
Poster here. I remembered that Chart::Strip jumps through all the necessary hoops to handle highly variable date ranges and data points. I'm going to take a crack and re-using that code and instead of generating its (relatively ugly) GD charts output using Open Flash Charts/Google Charts. Seems like it's going to be a little rough though.	[reply]