Python plot data against date

Question

I have a dataset:

          A     B      C    D    yearweek
    0    245    95    60    30   2014-48
    1    245    15    70    25   2014-49
    2    150   275   385   175   2014-50
    3    100   260   170   335   2014-51
    4    580   925   535  2590   2015-02
    5    630   126   485  2115   2015-03
    6    425    90   905  1085   2015-04
    7    210   670   655   945   2015-05

How to plot each value against 'yearweek'?

I tried for example:

    import matplotlib.pyplot as plt
    import pandas as pd

    new = pd.DataFrame([df['A'].values, df['yearweek'].values])
    plt.plot(new)

but it doesn't work and shows

    ValueError: could not convert string to float: '2014-48'

Then I tried this:

    plt.scatter(df['Total'], df['yearweek'])

turns out:

    ValueError: could not convert string to float: '2015-37'

Is this means the type of yearweek has some problem? How can I fix it?

Or if it's possible to change the index into date?

what is your expected result? can you provide an example? and what "dataset" is used? is that a standard class? — EvilSmurf
– EvilSmurf, Commented Oct 25, 2017 at 11:22

scholi · Accepted Answer · 2017-10-25 12:39:37Z

1

The best solution I see is to calculate the date from scratch and add it to a new column as a datetime. Then you can plot it easily.

df['date'] = df['yearweek'].map(lambda x: datetime.datetime.strptime(x,"%Y-%W")+datetime.timedelta(days=7*(int(x.split('-')[1])-1)))

df.plot('date','A')

So I start with the first january of the current year and go forward 7*(week-1) days, then generate the date from it.

answered Oct 25, 2017 at 12:39

scholi

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5 Comments

scholi Over a year ago

Usually you parse datetime with pandas.to_datetime, with a format string. Unfortunatelly "%Y-%W" or "%Y-%U" always return the first of January of the given year

Jenny Over a year ago

Before I do want to calculate it but failed. =p This seems a good solution, thank you as well!

Jenny Over a year ago

I tried this way, but there is an error: {ValueError: time data '2014-W48' does not match format '%Y-%W'}. I think it's because I saved year and week together as {year + '-W' + week}. Will it work if I move the '-W' part?

scholi Over a year ago

@Jenny, then you should adjust the format to match your data. If you have something like "2014-W48", then use "%Y-W%W" as a format.

scholi Over a year ago

For information, the above mentionned solution of Vivek does NOT work as expect. It just plot the x-axis as every week in a row. If you have missing weeks or jumps in the years or data entered in the wrong order, this will fail. Just try with yearweek=['2014-49','2014-48','2016-50'] (in this order)

Vivek Kalyanarangan · Accepted Answer · 2017-10-25 11:27:49Z

1

As of pandas 0.20.X, you can use DataFrame.plot() to generate your required plots. It uses matplotlib under the hood -

import pandas as pd
data = pd.read_csv('Your_Dataset.csv')

data.plot(['yearweek'], ['A'])

Here, yearweek will become the x-axis and A will become the y. Since it's a list, you can use multiple in both cases

Note: If it still doesn't look good then you could go towards parsing the yearweek column correctly into dateformat and try again.

answered Oct 25, 2017 at 11:27

Vivek Kalyanarangan

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