Plotting a graph using matplotlib with two lists

Question

I am trying to plot a graph after having imported data from a CSV file and stored it as two separate lists. Is it possible for matplotlib to plot a graph using a list of strings, or is it necessary for the lists two be lists of "int" ? If not, why is the following code not working?

Error prompted:

invalid literal for int() with base 10: '02_13_2014'

My code:

 import csv
    import numpy as np
    from numpy import genfromtxt
    import matplotlib.pyplot as plt
    import matplotlib.dates as mdates

with open('pytdef.csv','r') as f:
    reader = csv.reader(f)
    for row in reader:
        print (row)

first_column= ['Date']
second_column = ['Value']
Date_list = []
Value_list = []

with open('pytdef.csv') as f:
    reader = csv.reader(f)
    for row in reader:
        Date_list.append(row[0])

with open('pytdef.csv') as f:
    reader = csv.reader(f)
    for row in reader:
        Value_list.append(row[1])

    print (Date_list)
    print (Value_list)

Date_list = list(map(int,Date_list))
print (Date_list)
print (Value_list)


fig = plt.figure()
plt.plot_date(x=Date_list, y=Value_list)
plt.show()

o-90 · Accepted Answer · 2014-03-09 18:38:00Z

3

I think the problem here is your date. The code here is a lot simpler if you just use pandas

#!/usr/bin/env python

%matplotlib inline

import pandas as pd
import matplotlib.pyplot as plt
from datetime import date

columns = ['dates', 'value']
data = pd.read_csv('/location_of_file/file_name.csv', header=False, names=columns)

I'm assuming your data looks something like this...

enter image description here

then format the date

data['dates'] = [date(int(x.split('_')[2]), int(x.split('_')[0]), 
    int(x.split('_')[1])) for x in data.dates]
plt.plot(data.dates, data.value);

enter image description here

answered Mar 9, 2014 at 18:38

o-90

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