Create a matrix from a .txt file with strings

Question

I need to create a matrix from a .txt file, the proble I'm having is that the .txt file has a LOT of information (maybe no that much, but I'm new on programming so I have problems dealing with it)... The file has:

• Client number
• Name
• Last name
• Age
• Single or married (S or M)
• Sex (M or F)
• Favourite animal

like this:

1 James Gordon 35 M M Dog
...
75 Julius Harrison 48 S M Cat

I managed to read the file and create a list for each one of the persons, but also it's needed to calculate the average of age, sex... I don't know how to separate each one of the elements so I can do the math. Here's the code so far.

infile=open("db.txt","r")
list=infile.read()

matrix=[]

raw = []
with open('db.txt','r') as f:
    for line in f:
        raw.append(line.split())

Answer 1

You are using a list of list (raw) to hold the data. You can use list index to access the data.

e.g. average age

ages = [r[3] for r in raw]
average_age = float(sum(ages))/len(ages)

Answer 2

Since you've created a 2D list, you can simply access the elements using X and Y coordinates. For example, to calculate the average of their ages, you can sum up the fourth element of each person's sublist. The following page offers several ways to do this:

Calculate mean across dimension in a 2D array

Answer 3

Depending on what things you're interested in doing with your matrix, it may be a good idea putting everything in a numpy array. You can slice objects in either axis more easily and numpy arrays are faster than transversing lists.

import numpy as np

# read file and store the file lines in `raw` as you have done above, then
matrix = np.array(raw, dtype=object)
matrix[:,3] = matrix[:,3].astype(int)

average = np.mean(matrix[:,3])

If you want to count how many males you have, you can count how many Ms you have in the gender column.

male_no = len(np.where(matrix[:,5] == 'M'))

However, an even better way for counting items, especially for animals, where you may have more than 1-2 options, you can use Counter from the collection package.

from collections import Counter

gender_count = Counter(matrix[:,5])
for key in gender_count.keys():
    print key, gender_count[key]