Reading values from csv and drawing bar chart with matplotlib in python

Question

I'm trying to read in a delimited csv called 'StabilityResults.csv' and create a bar plot of column 7 with x-labels from column 0. Getting the labels from column 0 is not a problem but reading the values from col7 into a list doesn't seem to work as a valid input in matplotlib. Is there a way to convert my list of values so they are readable in matplotlib??

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

res = csv.reader(open('StabilityResults.csv'), delimiter=',')
res.next() # do not read header

mut = []
tot = [] 
a = 0
width = 0.2

for col in res:
    mut.append(col[0])
    tot.append(col[7])
    a += 1

ind = arange(a)

p1 = plt.bar(ind,tot,width,color='r')
labs = plt.xticks(ind+width,mut)

plt.show()

I also reading column7 using numpy's genfromtxt function but this gave an array which also didnt work.

tot2 = np.genfromtxt('StabilityResults.csv', delimiter=',', dtype=None, names=True, deletechars=',', usecols=[7])

Normally with genfromtxt it should work. What error message dit you get? — joris
– joris, Commented Mar 30, 2011 at 14:21

Manuel · Accepted Answer · 2011-03-30 11:15:05Z

1

You should convert the data to integer type (or float)

tot.append(int(col[7]))

answered Mar 30, 2011 at 11:15

Manuel

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Comments

sat_s · Accepted Answer · 2011-03-30 11:19:52Z

1

Ahh, should've spent more time. Similar to Manuel's answer, I just added a temporary holder to convert to a float in the for loop:

for col in res:
    tmp_tot = float(col[7])
    tot.append(tmp_tot)

Both ways work!

Cheers

answered Mar 30, 2011 at 11:19

sat_s

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Comments

eumiro · Accepted Answer · 2011-03-30 11:14:37Z

0

mut.append(col[0])
tot.append(col[7])

You append the content of col list, which is text. You will have to convert it to int or float:

mut.append(float(col[0]))
tot.append(float(col[7]))

edited Mar 30, 2011 at 11:14

answered Mar 30, 2011 at 11:07

eumiro

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