如何使用matplotlib读取文本文件和绘图

Question

This is my first time using python and matplotlib and I'd like to plot data from a CSV file.

The CSV file is in the form of:

10/03/2018 00:00,454.95,594.86

with about 4000 rows. I'd like to plot the data from the second column vs the datetime for each row and the data from the third column vs the datetime for each row, both on the same plot.

This is my code so far but it's not working:

import matplotlib.pyplot as plt
import csv
import datetime
import re
T = []
X = []
Y = []
with open('Book2.csv','r') as csvfile:
    plots = csv.reader(csvfile, delimiter=',')
    for row in plots:

        datetime_format = '%d/%m/%Y %H:%M'
        date_time_data = datetime.datetime.strptime(row[0],datetime_format)
        T.append(date_time_data)
        X.append(float(row[1]))
        Y.append(float(row[2]))

        plt.plot(T,X, label='second column data vs datetime')
        plt.plot(T,Y, label='third column data vs datetime')

        plt.xlabel('DateTime')
        plt.ylabel('Data')
        plt.title('Interesting Graph\nCheck it out')
        plt.legend()
        plt.show()

Any help or guidance would be great. Many thanks! :)

Answer 1

You could use pandas to read the CSV file

import pandas as pd

data = pd.read_csv('file_name.txt', header = None)

From there you can use the pandas dataframe as your input for matplot. A good tutorial can be found here

Answer 2

I hope this help you:

import csv
import numpy as np


a = []
with open('table.csv') as f:  # Let's say your data is at 'table.csv'
    f_csv = csv.reader(f)
    for row in f_csv:
        a.append(row)  # Get each line

b = np.array(a)  # Make it as a numpy array
c = b[:,[1,2]]  # Filter it by column

print(c)

Answer 3

import matplotlib.pyplot as plt
import csv

x = []
y = []

with open('example.csv','r') as csvfile:
    plots = csv.reader(csvfile, delimiter=',')
    for row in plots:
        x.append(float(row[2]))
        y.append(float(row[3]))

plt.plot(x,y, label='Loaded from file!')
plt.xlabel('x')
plt.ylabel('y')
plt.title('Interesting Graph\nCheck it out')
plt.legend()
plt.show()

dont forget to change the name of the file in my exemple or put the correct path if you are opening the file from different location if your file have float value change x.append(int(row[0])) to x.append(float(row[0])) and same for y