How do I create a heat map from three lists in python?

I have 3 arrays of data: initial_R, initial_v and E_total.

   import numpy as np
   import matplotlib
   import matplotlib as mpl
   import matplotlib.pyplot as plt
   import seaborn as sns
   import pandas as pd
   
   initial_R=[]
   initial_v=[]
   E_total=[]

I then have a piece of code that fills these three arrays. I wont post it here as its quite long, but it works.

initial_R is the x-coordinate, initial_v is the y-coordinate and E_total is the intensity value at those coordinates. I would like to plot this as a simple heatmap, with each square coloured one of two colours depending on if E_total is positive or negative.

    df = pd.read_clipboard()
    df.drop_duplicates(['initial_R','initial_v'], inplace=True)
    pivot = df.pivot(index='initial_R', columns='initial_v', values='E_total')
    ax = sns.heatmap(pivot,annot=True)
    plt.show()

    print (pivot)

I have seen the above code used before, but it doesn't work with my data, not sure how it works to be honest.

You can use numpy.sign to get the sign of your values:

import pandas as pd
import seaborn as sns

df = pd.DataFrame({'initial_R': [1, 2, 3, 1, 3, 1, 2],
                   'initial_v': [0, 0, 0, 1, 1, 2, 2],
                   'E_total': [-1, 2, -4, -3, 0, -1, 5]})

df.drop_duplicates(['initial_R','initial_v'], inplace=True)

pivot = df.pivot(index='initial_R', columns='initial_v', values='E_total')

sns.heatmap(np.sign(pivot), annot=True)

If you want to combine 0 and positive values:

sns.heatmap(pivot.ge(0).astype(int).mask(pivot.isna()), annot=True)

Output 1:

Output 2:

If you want custom labels:

pivot2 = pivot.ge(0).astype(int).mask(pivot.isna())

sns.heatmap(pivot2, annot=pivot2.replace({0: 'negative', 1: 'positive'}), fmt='s')

Output: