Python3 MatPlotLib : How can I get Multiple Line Plots

Question

I have a list of Tuples like this :

list_months = [ ('A', 'January'),
                ('A', 'January'),
                ('A', 'January'),  # Total 10 instances of ('A', 'January')
                ('A', 'March'),
                ('A', 'March'),
                ('A', 'March'),
                ('A', 'February'),
                ('A', 'February'),
                .............
                ('B', 'January'),
                ('B', 'January'),  # Total 15 instances of ('B', 'January')
                ('B', 'July'),
                ('B', 'July'),
                ............. ]

This was obtained via a Pandas dataframe using :

for index, val in b['Incident Reported Date Time'].iteritems():
    list_months.append((index, str(val)))

I want to be able to generate a MatPlotLib graph such that :
X-Axis -> Months
Y-Axis -> Volume
Multiple Colored Lines -> Each representing 'A', 'B', 'C', etc.

For example in this picture the Red line would represent 'A' and the blue line 'B'.
Since there are 10 of ('A', 'January') it shows the red line on 10 at the Y-Axis for the month of January and there are 15 of ('B', January') so it shows the blue line at 15 at the Y-Axis for the month of January.

How can I generate this and the legend dynamically in matplotlib for Python3 ?
The graph should be line graphs like in the example image.

I suggest you look at pandas. If you store your data in a pandas DataFrame you will be able to use its grouping and plotting abilities to do this task. — BrenBarn
– BrenBarn, Commented Aug 2, 2015 at 21:59
I extracted the data from pandas into a list of tuples to make it easier to plot. The data is originally from 2 columns of a Pandas dataframe. Using the command for index, val in b['Incident Reported Date Time'].iteritems(): list_months.append((index, str(val))) — Meghdeep Ray
– Meghdeep Ray, Commented Aug 2, 2015 at 22:07
Hint: It's just matplotlib, not MatPlotLib. Check the website. — MattDMo
– MattDMo, Commented Aug 3, 2015 at 0:57

Community · Accepted Answer · 2020-06-20 09:12:55Z

3

It will be easier to plot if you leave the data in a DataFrame. I made a sample DataFrame using the example data from your post:

list_months = [ ('A', 'January'),
                ('A', 'January'),
                ('A', 'January'),  # Total 10 instances of ('A', 'January')
                ('A', 'March'),
                ('A', 'March'),
                ('A', 'March'),
                ('A', 'February'),
                ('A', 'February'),
                ('B', 'January'),
                ('B', 'January'),  # Total 15 instances of ('B', 'January')
                ('B', 'July'),
                ('B', 'July')
            ]
d = pandas.DataFrame(list_months, columns=["Item", "Month"]).fillna(0)

>>> d
   Item     Month
0     A   January
1     A   January
2     A   January
3     A     March
4     A     March
5     A     March
6     A  February
7     A  February
8     B   January
9     B   January
10    B      July
11    B      July

Then you can get your plot easily:

>>> d.groupby(['Month', 'Item']).size().unstack().loc[['January', 'February', 'March', 'July']].fillna(0).plot(kind='line')

(The .loc['January', 'February', ...] bit is only necessarily to get the months in temporal order rather than alphabetical order. In the long run, you're probably better off storing this information via a datetime object or a number representing the month.)

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Aug 2, 2015 at 22:27

BrenBarn

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3 Comments

Meghdeep Ray Over a year ago

How would the code be different if I had a column for date time objects and had to convert it to show monthwise in the graph ?

BrenBarn Over a year ago

@MeghdeepRay: If you have a question about how to plot data with datetime objects, the best thing is to ask a separate question in which you provide sample data with datetime objects.

Meghdeep Ray Over a year ago

I put up a follow up question, would be grateful if you could help : stackoverflow.com/questions/31777482/…

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