How to read data from a file with a nonstandard separator and plot the values

Question

I've got a .txt file containing numbers like the following:

No. --- Amount -------- Location

1 ----- 23.5 -------- -0.0039

3 ----- 2.093 -------- 0.992

7 ----- 1.211 -------- 0.3929

5 ----- 0.898 -------- -1.8933

and so on

I've got approx. 700 numbers. Now I want to plot and visualize those numbers. To be exact: I want to show the "Amount" on the x-Axis and the "Location" on the y-Axis. The graph should resemble a sine curve. Moreover, I want to choose certain numbers. For example, only No. 1 and No. 2. That means, I need to read in the Amount and the Location of Number 1 and Number 2.

I have never worked before with Python or with Matplotlib. Since I hope that somebody could help me out or give me some hints.

So far, I've got the following code:

import matplotlib.pyplot as plt
import numpy as np
import io

numbers_file = open('numbers_file.txt').read().replace(',',' ')
numbers_data = np.loadtxt(io.StringIO(numbers_file),skiprows=1)

x = np.linspace(0, 2*np.pi, 20)
y = np.sin(x)
beta = x

plt.figure(figsize=(7,3))
plt.title('Companies amount and location')
plt.plot(x,y, label=r'sin( $\beta$ )')

plt.xlabel(r'$\beta$')
plt.ylabel('Location')
plt.legend()
plt.grid()

plt.show()

Beyond that, I want to use a specific textfile entry as a Start Point and as an End Point for my data graph. Some entries (access via 'No.' in the text file) should be visualized as maximum and as a minimum.

I would be very thankful for every help I can get because I am kinda lost on how to solve that.

Answer 1

• The easiest way to load the file, considering the unconventional separator, is to create a pandas.DataFrmae with pd.read_csv, which can have a regular expression for the separator.
  • Don't specify sep and engine if the separator is a ,
• The data can then be plotted with pandas.DataFrame.plot, which uses matplotlib as the default backend.
• There are many ways to select values based on another column, which are covered by other answers.
  • extract column value based on another column pandas dataframe
  • How do I select rows from a DataFrame based on column values?
  • Pandas select rows and columns based on boolean condition
    • selected = df[df['No.'].isin([1, 7])]
• Tested in python 3.9.7, pandas 1.3.4, matplotlib 3.4.3

import pandas as pd

# read the data in from the file
df = pd.read_csv('numbers_file.txt', sep=' -* ', engine='python')

# display(df)
   No.  Amount  Location
0    1  23.500   -0.0039
1    3   2.093    0.9920
2    7   1.211    0.3929
3    5   0.898   -1.8933

# plot
ax = df.plot(x='Amount', y='Location')

ax = df.plot(kind='scatter', x='Amount', y='Location')