I don't know if this is helpful or not, but I've seen some complaints
in the archives about a problem that I've been facing, so I thought
I'd post my solution.
I am auto-generating graphs of weekly data. In terms of pixels the
graphs will always be the same size, but the number of weeks included
can vary from a single week to two year's worth of data. For many of
these graphs matplotlib does a fine job of placing ticks in a helpful
and readable manner. But for some situations where I have say, six
weeks of data, it places ticks every few days in such a way that they
overlap and are unreadable.
The MaxNLocator is helpful in this situation as I can use it to limit
the number of ticks, but it isn't ideal because I really only want
the first day of the week labeled, not some arbitrary location in the
middle of the weeks. So I can up with the following locator that
will place a limited number of labels at places along the axis that
make sense. You pass it the max number of bins and the width of the
data. So for my needs I give it 6 bins and a width of 7 for weekly
data. If there are fewer dates then it only labels the start of each
week, not days in between. It there are more weeks than that it
tries to group them into 6 or fewer bins. I've done some testing and
it works well for me.
class MaxNDateLocator(Locator):
def __init__(self, num_bins, item_width):
self.bins = num_bins
self.width = item_width
def __call__(self):
self.verify_intervals()
vmin, vmax = self.dataInterval.get_bounds()
delta = vmax - vmin
mul = 1
if (mul*self.bins*self.width < delta):
mul = int(delta/(self.bins*self.width)) + 1
return range(vmin,vmax+1,mul*self.width)
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