Python plot misaligned labels and colors in legend

Question

I have a dataframe with many columns and data as given below:

rse_df

           Vstart=29V        Vend=37V  ...      Vstart=36V      Vend=37V
0          4.174279            1.0  ...         0.517509            1.0
1          4.032258            1.5  ...              NaN            NaN
2          3.509288            2.0  ...              NaN            NaN
3          3.091149            2.5  ...              NaN            NaN
4          2.746441            3.0  ...              NaN            NaN
5          2.439879            3.5  ...              NaN            NaN
6          2.305721            4.0  ...              NaN            NaN
7          2.057234            4.5  ...              NaN            NaN
8          1.826651            5.0  ...              NaN            NaN
9          1.634388            5.5  ...              NaN            NaN
10         1.479945            6.0  ...              NaN            NaN
11         1.347369            6.5  ...              NaN            NaN
12         1.238585            7.0  ...              NaN            NaN
13         1.106522            7.5  ...              NaN            NaN
14         0.990119            8.0  ...              NaN            NaN

I have plotted and the result is given below:

In plot-legend, all are wrongly represented. If you observe first label 'Vstart=29V' in plot-legend, it is wrongly represented. From dataframe, 'Vstart=29V' column data is represented in top line in pink color but legend says blue color, which is wrong. Looks like something is wrong here.

My code is:

plt.plot(rse_df[rse_df.columns[1::2].values],rse_df[rse_df.columns[0::2].values],'-o',markerfacecolor='none')  
plt.legend(rse_df.columns[0::2].values.tolist(),fontsize=8,ncol=1)

what is wrong in the above code causing this wrong alignment?

Approach1:

sns.lineplot(x=rse_df[rse_df.columns[1::2].values],y=rse_df[rse_df.columns[0::2].values], markers=True)
plt.show()

Output:

raise ValueError('If using all scalar values, you must pass'

ValueError: If using all scalar values, you must pass an index

Answer 1

Use seaborn:

• seaborn.lineplot has a number of parameters to customize what data is given to the function, including x and y parameters.

import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns

print(df)

 Vstart=29V  Vstart=30V
   4.174279    2.726868
   4.032258    2.420029
   3.509288    2.158159
   3.091149    1.916360
   2.746441    1.816749
   2.439879    1.618786
   2.305721    1.462994
   2.057234    1.328884
   1.826651    1.212548
   1.634388    1.112656
   1.479945    1.027790
   1.347369    0.921890
   1.238585    0.846886
   1.106522         NaN
   0.990119         NaN

sns.lineplot(data=df, markers=True)
plt.show()

Your code:

• You have misaligned the plot columns and the legend columns (e.g. [1::2] vs. [0::2])
• Also, this code doesn't match the plot in the question
  • This code plots Vstart=30V vs. Vstart=29V
• The plot shown in the question, plots all the data on the y-axis, with the index as the x-axis.

plt.plot(df[df.columns[1::2].values], df[df.columns[0::2].values], '-o', markerfacecolor='none')  
plt.legend(df.columns[0::2].values.tolist(),fontsize=8,ncol=1)

Plot generated with the code provided in the question:

This plot with seaborn

sns.lineplot(x='Vstart=30V', y='Vstart=29V', data=df)