Python: CSV to Barchart using Matplotlib

Question

I would like to draw a Bar chart from a CSV file which has the following format:

#Number of Occurrences, Occurrences of A, Occurrences of B, Occurrences of C
30,1,3,26
...

I am totally new to Matplotlib and I'm trying to understand how to do it. I wish for the y Axis to have the #Number of Occurences value (30 for the provided example), and three bars; The bar A,B and C with the respective values.

How could I do it?

My Code:

#!/usr/bin python



import matplotlib.pyplot as plt
import pandas as pd
import numpy as np
import sys

def main():

    table  = pd.read_csv(sys.argv[1])

    final = table.tail(1)

    names_list = list(final)
    values     = [ final.values[0][1], final.values[0][2], final.values[0][3] ]

    position = np.arange(len(names_list)) 

    plt.title(sys.argv[1].split('.')[0])

    plt.bar(position,values,align='center')

    plt.yticks(position,names_list)

    plt.show()



if __name__ == '__main__':
    main()

But I get **ValueError: shape mismatch: objects cannot be broadcast to a single shape**

Answer 1

The error is because 'values' has 3 values on it, and position has 4 values on it. So, shape mismatch. There are also other things with x and y axis. Check this code and let me know if it does what you expect:

def main():

    table  = pd.DataFrame([[30, 1, 3, 26]], columns=['Number Oc', 'Oc A', 'Oc B', 'Oc C'])

    final = table.tail(1)

    names_list = list(final)
    values     = [ final.values[0][1], final.values[0][2], final.values[0][3] ]

    position = np.arange(len(names_list)-1)

    plt.title(sys.argv[1].split('.')[0])

    plt.bar(position,values,align='center')

    plt.xticks(position, names_list[1:4])

    plt.show()

Answer 2

ValueError: shape mismatch: objects cannot be broadcast to a single shape

---

Debug your code:

1. Watch len(position)
2. Watch len(values)
3. Compare len(position) and len(values)
4. You can find your len(position)!=len(values)
5. matplotlib.pyplot.bar(x, height) require “The x coordinates of the bars and The height(s) of the bars should have the same length.”

So you should keep the lengths of the two arrays consistent according to your needs.