How to Order Y Axis Values in Matplotlib When They Initially Appear Unordered?

Matplotlib Y Axis Values Remain Unordered

Problem Statement

When plotting data using Matplotlib, it's common to encounter a situation where the Y axis values appear unordered. This can lead to confusion when interpreting the chart.

Detailed Analysis

The issue arises when the data on the Y axis is treated as strings instead of numerical values. Matplotlib automatically attempts to sort strings alphabetically, which can disrupt the expected ordering of the data.

Solution

To resolve this issue, convert the Y axis data to numerical values before plotting. This can be achieved by using the following steps:

1. Extract the Y axis data as strings.
2. Convert each string value to a float or an integer.
3. Create a NumPy array from the converted values.
4. Use the NumPy array to plot the data on the Y axis.

Example

Consider the following code snippet:

<code class="python">import matplotlib.pyplot as plt
import numpy as np

# Extract Y axis data as strings
solar = [line[1] for line in open('PV5sdata1.csv')][1:]

# Convert strings to floats
solar = [float(data) for data in solar]

# Create a NumPy array
solar_array = np.array(solar)

# Plot using NumPy array
plt.plot_date(Time1, solar_array, 'k-')</code>

By converting the solar data to floats before plotting, the Y axis values will be treated as numerical values and ordered correctly.

Additional Enhancements

In addition to converting the data, it's recommended to use Matplotlib's auto formatting for the X axis when using dates or times. This can improve the appearance of the chart by rotating the labels and adjusting their orientation.

<code class="python">plt.gcf().autofmt_xdate()</code>

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