How to read strings from a csv file and convert it into a integer array?

Question

I am finding the most optimized way to create an integer array with the help of data from a csv file.

The csv file("sample.csv") data is like,

prediciton1	prediction2	prediction3
low	low	low
low	high	high

where low = 1, high = 3,

i want to read these data from the csv and make an array that looks like,

array =  
[[1,1,1],  
[1,3,3]]


    import csv
    import sys
    
    num1 = 'low'
    num2 = 'high'
    
    
    csv_file = csv.reader(open('sample.csv', "r"), delimiter=",")
    
    count = 0
    
    for row in csv_file:
    
        if count == 1:
            if num1 == row[0]:
                dat1 = 1
        
            elif num2 == row[0]:
                dat1 = 3
            if num1 == row[1]:
                dat2 = 1
        
            elif num2 == row[1]:
                dat2 = 3
                
            if num1 == row[2]:
                dat3 = 1
        
            elif num2 == row[2]:
                dat3 = 3
        
            
        count = count + 1

    array =[dat1,dat2,dat3]

This approach works but seems much inefficient. Finding an alternative and optimized way to achieve this.

Rakesh · Accepted Answer · 2021-05-23 09:42:14Z

3

Using a dict for a lookup and list comprehension

Ex:

check = {'low': 1, "high": 3}

with open('sample.csv') as infile:
    csv_file = csv.reader(infile)
    next(csv_file) # skip header
    result = [[check[c] for c in row] for row in csv_file]

answered May 23, 2021 at 9:42

Rakesh

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1 Comment

The Punisher Over a year ago

Nice and clean solution! I would only add that, just in case the CSV contains unwanted values (as it sometimes may happen) I would use check.get(c) instead of check[c] and so handle later the potential None values contained in the result array.

The Punisher · Accepted Answer · 2021-05-23 09:47:37Z

1

As the CSV file is pretty simple, you could even do it without the CSV package:

# We open the CSV file
with open('sample.csv') as file:
    # We read all the lines and store them in a list
    lines = file.readlines()

# We remove the CSV header
lines = lines[1:]

# We create the array
array = [
    [{
        'low': 1,
        'high': 3
    }.get(value.strip()) for value in line.split(',')
] for line in lines]

# We print the array
print(array)

This would print the following array: [[1, 1, 1], [1, 3, 3]]

Note the use of the dict's get method to avoid errors just in case the CSV has unwanted values. The array would contain a None value in those cases.

answered May 23, 2021 at 9:47

The Punisher

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