Using matplotlib to graph rows by column of a csv file

Question

Very new at Python and first time using matplotlib

I'm trying to graph a multiline plot based on the rows of a CSV file.

CSV file looks something like this:

Row1        S1      S2     S3      HWS
Row2        2.45    3.76   2.44    1
Row3        3.59    2.56   9.68    2
Row4        2.54    9.45   6.78    3

I want to graph the HWS values by each row in the csv file.

Ex: For Row2, I want my points to be (1, 2.45), (2, 3.76), and (3, 2.44). For Row3, I want my points to be (1, 3.59), (2, 2.56), and (3, 9.68).

I've already looked at modules like pandas from other stack overflow answers, but I can't find commands to graph by rows. All I found is ways to graph a whole CSV file or ways to isolate columns of a csv file.

Is there a way to graph this way using Python and matplotlib?

kaminsknator · Accepted Answer · 2015-07-30 21:27:54Z

2

Read in each column in the csv into separate lists.

plotting the data is trivial. Here's a basic example in your code the data sets come from the csv.

import matplotlib.pyplot as plt

s1 = [2,3,2]
s2 = [3,2,9]
s3 = [2,9,6]
hws = [1,2,3]

plt.plot(hws,s1)
plt.plot(hws,s2)
plt.plot(hws,s3)

answered Jul 30, 2015 at 21:27

kaminsknator

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2 Comments

whent1991 Over a year ago

I have a huge dataset - is there a way for me to read the specific columns s1, s2, s3... I can't manually type them. Thanks!

kaminsknator Over a year ago

yes there most certainly is. At this point in the discussion, referencing the teach a man to fish etc, you'll find it beneficial to try googling "how to read a csv with python". In fact this question could have found a solution using this method as well. Best of luck to you.

Amritbir Singh Gill · Accepted Answer · 2015-07-30 22:54:01Z

1

Try this if you have a huge dataset.!

import csv
import matplotlib.pyplot as plt
import os

os.chdir(r"C:\--")  #path of your csv file

S1=[]
S2=[]
S3=[]
HWS=[]
with open('dataSet.csv','r') as csvFile:
    reader=csv.reader(csvFile,delimiter=';')
    next(reader)
    for row in reader:
        temp=row[0]
        S1.append(temp)
        temp=row[1]
        S2.append(temp)
        temp=row[2]
        S3.append(temp)
        temp=row[3]
        HWS.append(temp)
plt.plot(HWS,S1)
plt.plot(HWS,S2)
plt.plot(HWS,S3)
plt.show()

answered Jul 30, 2015 at 22:54

Amritbir Singh Gill

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8 Comments

whent1991 Over a year ago

This solution looks great - but I get an error when I try to run it: IndexError: list index out of range i know it probably doesn't have to do with the code, but if you know, could you shed some light as to why this error is happening?

Amritbir Singh Gill Over a year ago

which version of python you are using.? try changing delimiter to ',', try 'rb' at the place of 'r' in 9th line and keep r before the path of your file in line 4

whent1991 Over a year ago

I'm using python 2.7.10

Amritbir Singh Gill Over a year ago

i am using 3, anyways try 'rb' at the place of 'r'.

whent1991 Over a year ago

still no luck...the error only appears when I add the code past "temp=row[0] S1.append(temp)"

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