Plotting graphs with empty elements in a list

Question

import matplotlib.pyplot as plt

x = [2.4, 3.2, 4.435, 5.65, 6.4, 7.333, 8.5, 9.2345]
y = [1.4356, "", 5.32245, 6.542, 7.567, .77558, "", ""]

y1 = [] 
for string in (y):
    if (string != ""):
        y1.append(string)

plt.plot(x, y1, 'b.', label="Sample data")
plt.show()

When I try to plot this I get Value Error "x and y must have same first dimension, but have shapes (8,) and (5,)"

I want to skip over these empty elements and plot just the 5 points but I don't know how to go about it.

because you skip the " (quote) so you change the size of the array — Beny Gj
– Beny Gj, Commented Apr 8, 2021 at 12:40
When I do include the empty elements, it shows up as 0. I don't want to plot the empty values as 0. I'm wondering if there's a way of ignoring the corresponding y component in order to just plot the 5 points that have both x and y values. — Amnesia Smith
– Amnesia Smith, Commented Apr 8, 2021 at 12:44

Otto Hanski · Accepted Answer · 2021-04-08 12:46:32Z

2

The plot command wants the x and y dimension arrays you give it to be the same size. But since y1 is simply y with some elements removed, the y1 list will have fewer elements than the list of x coordinates. An easy workaround is to simply create also an x1 list, where you add the x coordinates matching the y1 coordinates, and plotting using x1 and y1.

Here's an example solution:

import matplotlib.pyplot as plt

x = [2.4, 3.2, 4.435, 5.65, 6.4, 7.333, 8.5, 9.2345]
y = [1.4356, "", 5.32245, 6.542, 7.567, .77558, "", ""]

x1 = []
y1 = [] 
for index in range(len(y)):
    if (y[index] != ""):
        y1.append(y[index])
        x1.append(x[index])

plt.plot(x1, y1, 'b.', label="Sample data")
plt.show()

Note that the loop was changed to loop by index, rather than the value of items in the list, since this lets us easily take the matching pairs of values from both lists.

answered Apr 8, 2021 at 12:46

Otto Hanski

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6 Comments

Amnesia Smith Over a year ago

I'm new to coding and had difficulty with this. Tysm!

Otto Hanski Over a year ago

No prob, no one is born a programmer, wish you luck with your project :)

Antonin Over a year ago

@AmnesiaSmith I think Otto's answer is good and solved your problem. You should now accept his answer by clicking on the green V on the left side.

Otto Hanski Over a year ago

@Antonin Personally I will admit I found the answer of Beny Gj more fitting from a data handling perspective, since his solution doesn't lose any data points, while still solving the problem at hand. Albeit I would've modified it to feed the NaN values back into the initial y list, rather than making a new list.

Amnesia Smith Over a year ago

@OttoHanski I tried this method with more y-values of missing data but it showed a dimensional error. Is there some way to bypass this without suing pandas?

|

Beny Gj · Accepted Answer · 2021-04-08 12:50:49Z

1

here you can use with numpy to put NAN instead of quote

#!/user/bin/env python
# -*- coding: utf-8 -*-
import matplotlib.pyplot as plt
import numpy as np

x = [2.4, 3.2, 4.435, 5.65, 6.4, 7.333, 8.5, 9.2345]
y = [1.4356, "", 5.32245, 6.542, 7.567, .77558, "", ""]

y1 = []
for string in (y):
    if string != "":
        string = np.NAN
    y1.append(string)


if __name__ == '__main__':

    plt.plot(x, y1, 'b.', label="Sample data")
    plt.show()

answered Apr 8, 2021 at 12:50

Beny Gj

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