Plot a vertical line using matplotlib in my plot

Question

I have a following problem. I have these data:

import pandas as pd, numpy as np

data = pd.DataFrame(
    {
        "year": [2000, 2001, 2001, 2001, 2002, 2003, 2004, 2005, 2006, 2007],
        "week": [0, 1, 2, 2, 3, 3, 4, 5, 6, 7],
        "value": [8, 1, 53, 2, 55, 3, 4, 55, 60, 76],
    }
)

Then I plot the data week_groups = data.groupby([data["year"], data["week"]])["value"].count()

Now I would like to add a vertical line in (2004, 4). I try plt.axvline(x=(2004, 4)) but I got an Error ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all().

This does not help either:

plt.axvline(data["year"][np.where(np.array(data["year"]) == 2004)[0][0]])
week_groups.plot(kind="bar", figsize=(10, 5))
plt.show()

How can I fix it please?

You must specify the index of (2020,20) for x, since (2020,20) is only the tick label — Benjamin T. Schwertfeger
– Benjamin T. Schwertfeger, Commented Jun 27, 2021 at 10:34
@ShaunHan does not help. It just put the line in the first index that is (2012, 13) — vojtam
– vojtam, Commented Jun 27, 2021 at 10:38

Tanmaya Meher · Accepted Answer · 2021-06-27 12:58:14Z

1

This might help.

# coding: utf-8
import pandas as pd
from matplotlib import pyplot as plt

data = pd.DataFrame(
    {
        "year": [2000, 2001, 2001, 2001, 2002, 2003, 2004, 2005, 2006, 2007],
        "week": [0, 1, 2, 2, 3, 3, 4, 5, 6, 7],
        "value": [8, 1, 53, 2, 55, 3, 4, 55, 60, 76],
    }
)

week_groups = data.groupby([data["year"], data["week"]])["value"].count()

for i in range(len(week_groups.index)):
    if week_groups.index[i] == (2004,4):
        plt.axvline(i, color='skyblue')
# Apparently, i can only solve this by a for loop. 
# Tried every other indexing method. But, no avail. 
# If any one can come up with a shorter / better code, you are welcome.
week_groups.plot(kind="bar", figsize=(10, 5))
plt.show()

Output below:

answered Jun 27, 2021 at 12:58

Tanmaya Meher

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1 Comment

Benjamin T. Schwertfeger Over a year ago

Nice! here is the one liner: plt.axvline([i for i in range(len(week_groups)) if week_groups.index[i]==(2004,4)][0], color='skyblue')

Benjamin T. Schwertfeger · Accepted Answer · 2021-06-27 10:53:02Z

0

I don't know exactly how your groupby object is structured, so I've written a little example that shows how to get a specific index from a dataset and plot a vertical line based on it.

import pandas as pd, numpy as np

data = {
  "year": [2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007],
  "week": [0, 1, 2, 3, 4, 5, 6, 7]
}
plt.axvline(data['year'][np.where(np.array(data['year']) == 2004)[0][0]])
plt.plot(data['year'], data['week'])

answered Jun 27, 2021 at 10:53

Benjamin T. Schwertfeger

2744 silver badges14 bronze badges

1 Comment

vojtam Over a year ago

I improved my question, please look on reproducible example. Thanks a lot

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