Re: [Matplotlib-users] Date plotting

[John H. <jdh...@ac...>]

>>>>> "Steve" == Steve Chaplin <ste...@ya...> writes:

    Steve> John, I've just started using the new tick locating,
    Steve> formatting and date plotting and noticed if you want to
    Steve> show day of month, month and year its quite easy to end up
    Steve> with major and minor tick labels overwriting each other.
    Steve> Is there a way to draw the major tick label underneath the
    Steve> minor tick label so they're not competing for the same
    Steve> space?

There are a few ways to go here.  First of all, with no change to the
code, you can set the tick positions of the minor tick labels as
follow.  I'm just winging this code so apologies if there is a minor
mistake somewhere

ax = subplot(111)

#your plot here
for tick in ax.xaxis.get_minor_ticks():
    tick.label1.set_y(-0.1)

Note that the y coord of the x tick label is in axes coordinates,
where 0 is the bottom and 1 is the top of the axes, so -0.1 is 10%
below the bottom of the axes.  label1 and label2 are the bottom and
top label text.Text instances (this is a recent feature to support
left/right labeling or top/bottom tick labeling) so you can call any
of the Text methods on them.

Note this code only affects the current ticks, so if you were doing
interactive navigation and zoomed out, thereby creating new minor
ticks, the new minor ticks would have their default locations (but I
can fix this fairly easily by updating the copy properties function
that transfers old tick properties to new ones when ticks are created
during interaction).

There is an additional consideration.  Currently, the tick drawing
code will skip a minor tick if a major tick has already been drawn at
that exact location.  In axis.py there is a line in the axis drawing
code that reads

            if seen.has_key(loc): continue

where seen is a dict that has a key if the tick location loc was drawn
by the major tick drawing code.  We could add an attribute, something
like forceDraw, to the tick and modify this code so that you could do

            if not tick.forceDraw and seen.has_key(loc): continue

and in your code

for tick in ax.xaxis.get_minor_ticks():
    tick.forceDraw = True
    tick.label1.set_y(-0.1)

Let me know how this works for you.

We could automate this a bit if you think it's worthwhile, eg by
setting a 'draw under' flag for the minor ticks, getting the bounding
boxes of the major ticks in the axis drawing code, and setting the
offsets automagically.  This would have the dual advantages of working
in the presence of changes in font size, interaction, etc.  The
question is whether it's sufficiently common to justify the extra work
or if the manual control approach above suffices.  If you want to add
this feature, I can get you some additional pointers to code showing
how to get the bounding box of all the major tick labels and using
this to control the positioning of the minor tick labels.

JDH