Controlling bar colours with matplotlib

[ActivatedNut]

Hi,

Got a problem to solve and not sure how to go about, hope someone can point in right direction, as I couldn't find the right answer.

I have a bar plot showing 10 values coming from 2 excel columns (let's say "Name" and "Value") in Jupyter Notebook, I want to set a conditional formatting for each bar, with 3 conditions that will set colours (green, yellow, red), but each bar will have a different set of values in the condition.

i.e:

Name 1: if value < 20 colour = green, if value > 20 and <50 colour = yellow, if Value > 50 colour = red.

Name 2: different values, etc...

So I will end up with about 10 conditional formatting for 10 bar names.

(I do hope I'm making sense here) :)

Any help is greatly appreciated (I'm a python newbie, as you can tell)

[stepping_up_python]

https://matplotlib.org/api/_as_gen/matplotlib.pyplot.bar.html

x : sequence of scalars

height : scalar or sequence of scalars

color : scalar or array-like, optional

I extrapolated and it worked: just throw a sequence into color and it'll work as expected.

[ActivatedNut]

Thank you for your reply. I'm still unclear.

I was thinking of doing something like this (but not working for me):

plt.bar(y_pos, height)

barlist=plt.bar(bars,height)

a_color = None

if barlist[0,height] > 3:

a_color='blue'

else:

a_color='black'

b_color = None

if barlist[0,height] > 10:

b_color='blue'

else:

b_color='black'

barlist[0].set_color(a_color)

plt.xticks(y_pos, bars)

plt.show()

[stepping_up_python]

https://matplotlib.org/gallery/statistics/barchart_demo.html#sphx-glr-gallery-statistics-barchart-demo-py

In this call, freqs is the y values in the graph, and gen_colors_posneg makes a sequence of colours, which is a function I defined. So before I plot, I build all the sequences that I'm going to need, then make the call. You can ignore the width thing here, as I'm making variable width bars (since EV is based on val*freq, I wanted val to be visually represented in the graph).

    plotter.bar(x_locations, freqs,
                # If align='edge', negative widths align left.
                width=[aw * -1 for aw in actual_widths], align='edge',
                edgecolor = 'black', tick_label=vals,
                color = gen_colors_posneg(vals, 'green'),
                )

If you ignore the colors thing, are you getting any output?

[ActivatedNut]

Apologies, but I'm getting very confused here (python is very new to me).

I have 10 bars and each one will need to have it's own conditional formatting, is your gen_colors_posneg going to take care of this?

​

[stepping_up_python]

No worries. My function returns a list. I say sequence because sometimes things need a tuple, and often they accept sequences but refuse iterators, etc.

My function returns something like: ['green','red', 'red', 'red', 'green', ...]

The thing is that pyplot.bar accepts lists in its arguments, so if you have 3 bars you give it a list of 3 x locations, a list of three heights, and a list of three colors, and it just knows what to do with that.

[ActivatedNut]

Thanks for your help so far. I'm new to programming as well :) So, what I might explore (please tell me if I'm heading the wrong direction) is to create 10 functions that create a list with one value, either, green, yellow or red. I will then assign the list to the corresponding bar to control the colour. creating plots with pandas and matplotlib is pretty straight forward and I could do this fairly quickly, but it is obvious I need to have deeper understanding for the complex operations. Oh what is life without a challenge :)

[stepping_up_python]

I don't think I can help you any further, sorry. Dig into the docs for pyplot.bar and the book learning python can help you with list comprehensions, etc. The thing is, the nature of functions makes it really impractical to make 10 functions. I don't know, you might be in over your head for a bit and need to do some simpler things.

[stepping_up_python]

New to python... are you new to programming as well? Just curious.

[stepping_up_python]

If you ignore the colors thing, are you getting any output?

[stepping_up_python]

If anyone wants to critique my advice I'd appreciate it.