How to create a list in python, add values, and take them out

Question

I'm new in python. I want to read data from a csv file, and then create a graph from those data. I have a csv file with 2 columns and 20 row. In the first row I have 1 1, second row have 2 2, and so on, until 20 20. I want to take this coordinates and make graph.

This is what I have so far:

import csv
from pylab import *

with open('test.csv', 'rb') as csvfile:
    spamreader = csv.reader(csvfile, delimiter=' ', quotechar='|') # open the csv file
    for row in spamreader:
        print ', '.join(row) #  in each loop, row is getting the data,
                             # first row is [1,1] , then [2,2] and so on

plot()
show()

Now, What I was thinking is to make row to be in the end, with 2 cols and 20 row with all data. Then I need to do parameter x, to be the first col, and y to be the second col, and give plot the x,y.

My problem is that I don't know how to save all values in row, and how to take only the first col and second col.

Thank you all!

shutos · Accepted Answer · 2013-11-27 09:28:14Z

1

You had problems in reading csv file
1) delimiter = ','

Regarding populating the x and y values for the graph. Just read the first and second values of each row and populate the x and y lists.

Here is the modified code:

import csv
from pylab import *

with open('test.csv', 'rb') as csvfile:
    spamreader = csv.reader(csvfile, delimiter=',', quotechar='|') # open the csv file
    x = []
    y = []
    for row in spamreader:
        x.append(row[0])
        y.append(row[1])
        print ', '.join(row) #  in each loop, row is getting the data,
                         # first row is [1,1] , then [2,2] and so on

plot(x, y)
show()

answered Nov 27, 2013 at 9:28

shutos

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1 Comment

shutos Over a year ago

Actually Vikash's answer is more elegant as "zip" is ideal for such kind of computation. The change of splitting the row with "," would work just fine. But since you are new to python I guess my answer would be easier to understand.

VIKASH JAISWAL · Accepted Answer · 2013-11-27 09:12:33Z

0

You can use this to get your X and Y axis:

with open('./test4.csv', 'rb') as csvfile:
    (X,Y) = zip(*[row.split() for row in csvfile])

answered Nov 27, 2013 at 9:12

VIKASH JAISWAL

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2 Comments

shlomi Over a year ago

Hi, I was doing this: import csv from pylab import * with open('test.csv', 'rb') as csvfile: (X,Y) = zip(*[row.split() for row in csvfile]) #spamreader = csv.reader(csvfile, delimiter=' ', quotechar='|') #for row in spamreader: # print ', '.join(row) plot() show() But I'm getting an error: (X,Y) = zip(*[row.split() for row in csvfile]) ValueError: need more than 1 value to unpack

VIKASH JAISWAL Over a year ago

that must be because of format of data. Just print this, [row.split() for row in csvfile] and let me know what do you get? If your values are separated by commas then instead split(',') will work.

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