[Chicago] Suggestions on improving histogram in matplotlib?

[Ryan Nelson]

Douglas,

First of all, to answer you specific comments:
* It is probably best not to use newline characters to move around the text
like that. You can adjust the axes (plot area) to give the title more room.
I couldn't reproduce your problem, though, so I can't comment directly on
what you expected to see.
* When you use an integer number to the hist bin keyword argument, you are
not necessarily going to get bins that start exactly at integer values. You
can however pass in a list (or array) of specific values that you want to
use. (See below)

Anyway, I rewrote your script in a different style. See attached. First of
all, Numpy is your friend. It is installed with Matplotlib, so you already
have it available. The dice roll calculation with Numpy is much faster and
the code is simpler. Also, for various reasons, you should create your
histogram as a separate function call, and probably as a first step. I've
never passed an argument to the show function, but there might be some
times when it is necessary. I also passed an align keyword argument to the
histogram function to align the bins on top of the ticks.

Hope that helps. The folks at the Matplotlib user email list are very
helpful.

Ryan

Numpy is your friend here.

>
>
> Message: 1
> Date: Fri, 20 Mar 2015 13:33:24 -0500
> From: "Lewit, Douglas" <d-lewit at neiu.edu>
> To: The Chicago Python Users Group <chicago at python.org>
> Subject: [Chicago] Suggestions on improving histogram in matplotlib?
> Message-ID:
>         <
> CAPdZZGwuY7XPhwckv14Pj3FwLXsTpMyDjR9ocXGkENz4M+CVLw at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hey there,
>
> I'm attaching my script (done in Python 3 but it should work almost the
> same in Python 2) and also a .png file that shows the resulting histogram.
> It looks really good!  However, a couple of comments or criticisms.  First
> off, if you look at my command *pyplot.title(.....)* you'll see that the
> title begins with "\n" (the newline character) but it doesn't cause an
> extra blank line above the title in my plot.  Any suggestions?  Or is that
> just a minor bug in matplotlib?
>
> Also, please note that the rectangles of the histogram are not squarely
> placed over the corresponding tickmarks, except when you get closer to the
> center of the histogram, around 11, 12, 13, 14, 15, 16, 17, 18, etc.  But
> further out the rectangles appear toward the side of the corresponding
> tickmark.  Again, I'm not sure if that's a true "bug" or maybe I'm just not
> interpreting the histogram properly or maybe that's how all histograms
> should be drawn!  I really don't know, but if you have any suggestions
> please let me know.
>
> In case you're wondering, this is the problem of rolling 4 dice and
> recording their sums.  So the smallest sum should be 4 (1 + 1 + 1 + 1) and
> the largest sum should be 24 (6 + 6 + 6 + 6).  The sum of 14 is the most
> probable of all the sums, with a probability of close to 12%.  The other
> sums are less probable, and the least probable sums of all are 4 and 24.
> The data look normally distributed with a mean of about 14, but I'm not
> sure about the variance and standard deviation.  I didn't bother to compute
> those, but they are probably not that difficult to compute from the raw
> data generated by Python.
>
> The script won't work unless you have matplotlib as part of your Python
> installation!  Matplotlib is pretty amazing, and produces graphics that are
> on par with Maple, Mathematica and Matlab.  (Matplotlib's plots look very
> "Matlabby" to me.  I'm not sure if that's a coincidence or if that was an
> intentional part of the design.  What do you think? )
>
> Okay, thanks!  I appreciate any constructive suggestions on improving the
> histogram so that it has professional textbook quality.
>
> Best,
>
> Douglas Lewit
>
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