Plotting graph from CSV

Question

Im looking for a bit of help, Im really new to Python and dont know if it just making thngs harder for myslef or what. Im trying to plot a simple line graph from a csv file. Ive tried a number of approaches but all return the error : ValueError: could not convert string to float:

This is the code if seeming to get the best with

import csv`
import pylab as pl
import numpy as np
matplotlib.dates as mdates
with open('D:/growth_rate.csv') as csvfile:
     readCSV = csv.reader(csvfile, delimiter=',')

for row in readCSV:
    print (row)
a= (row)
np.shape(a)
x,y = np.loadtxt('D:/growth_rate.csv', delimiter = ',', unpack=True,
                         converters = {0: mdates.strpdate2num('%d/%m/%Y')})

Ive also tried the csv reader approach, but similar problem

a = zip(*csv.reader(open('D:/growth_rate.csv', 'rb')))
csv.writer(open('D:/growth_rate.csv', "wb")).writerows(a)

print a

I dont know if its a problem with the csv file, it originally was a xls file, with a company headers and other nonsense, so i put it into a csv and also tried a txt file. Either that or im missing something really obvious,

Any help, greatly appreciated.

can you post part of your CSV file or better a link to it or to excel file so we could download it and try to develop a working solution? — MaxU - stand with Ukraine
– MaxU - stand with Ukraine, Commented Apr 16, 2016 at 23:29
uploaded it to onedrive, let me know if the link works. Cheers onedrive.live.com/… — anthony mccool
– anthony mccool, Commented Apr 16, 2016 at 23:36
there are no values in first two rows - is it OK? and how do you want to plot it as a line or as bars? Is it OK for you to use pandas module? - it's going to be much easier — MaxU - stand with Ukraine
– MaxU - stand with Ukraine, Commented Apr 16, 2016 at 23:38
yehm theres no data for the first two dates, yeh if it pandas works then thats great — anthony mccool
– anthony mccool, Commented Apr 16, 2016 at 23:46

or1426 · Accepted Answer · 2016-04-17 00:02:29Z

2

You can also do this in numpy / matplotlib without needing pandas. Note that np.genfromtxt can cope with blank lines fine (as opposed to np.loadtxt which will break. By default those values get filled with NaNs but you can change this with the filling_values option.

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

date_decode_function = lambda b: mdates.strpdate2num('%d/%m/%Y')(b.decode())

dates, growth_rates = np.genfromtxt('growth_rate.csv',
                                    delimiter = ',',
                                    unpack=True,
                                    converters = {0: date_decode_function})


fig, ax = plt.subplots()
ax.plot_date(dates, growth_rates,'-',lw=2)
plt.xlabel("Date", fontsize=16)
plt.ylabel("Growth rate", fontsize=16)

plt.grid()
plt.show()

answered Apr 17, 2016 at 0:02

or1426

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3 Comments

anthony mccool Over a year ago

Thats working. Brilliant. Is there any way i can have multiple graphs on the one output? Separate graphs but as if it was for the one print out. The csv file i uploaded is a smaller section of a bigger file

or1426 Over a year ago

@anthonymccool You need to use the plt.subplot method. The exact invocation will depend on what you're trying to accomplish but the examples here should help.

anthony mccool Over a year ago

yeh something similar to that output, ill have a wee tinker and see what i come up with. Thanks everyone, really helped me out there

MaxU - stand with Ukraine · Accepted Answer · 2016-04-16 23:48:18Z

0

pandas approach:

import pandas as pd
import matplotlib as plt

fn = r'D:\temp\.data\growth_rate.csv'
#df = pd.read_csv(fn, parse_dates=[0], names=['date','val']).set_index('date')
df = pd.read_csv(fn, names=['date','val']).set_index('date')

# bar plot
df.plot(kind='bar')

# line plot
#df.plot()

plt.show()

answered Apr 16, 2016 at 23:48

MaxU - stand with Ukraine

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