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.

Answer 1

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()

Answer 2

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()