I am struggling with an issue regarding CSV files and Python. How would I generate a random number in a csv file row, based of a condition in that row.

Essentially, if the value in the first column is 'A' I want a random number between (1 and 5). If the value is B I want a random number between (2 and 6) and if the value is C, and random number between (3 and 7).

CSV File

Thanks in advance

The only thing I have found was creating a new random number dataframe. But I need to create a random number for an existing df.

CodePudding user response：

One of the ways is to use numpy.random.randint with numpy.select :

import pandas as pd
import numpy as np

df = pd.read_csv("inputfile.csv", sep=",")
#change the separator according to the actual format of your csv

categories = [df["Letter"].eq("A"),
              df["Letter"].eq("B"),
              df["Letter"].eq("C")]
​
#random.randint(low, high=None, size=None, dtype=int)
choices = [np.random.randint(1, 5 1),  #high is exclusive
           np.random.randint(2, 6 1),  #high is exclusive
           np.random.randint(3, 7 1)]  #high is exclusive

#numpy.select(condlist, choicelist, default=0)​
df["Random Number"] = np.select(categories, choices)

# Output :

print(df)

  Letter  Color  Random Number
0      A  Green              5
1      C    Red              6
2      B    Red              5
3      B  Green              5
4      C   Blue              6

If needed, you can use pandas.DataFrame.to_csv to generate a new (.csv) :

df.to_csv("output_file.csv", sep=",", index=False)

CodePudding user response：

Here is a simple way doing it without using pandas. this program modifies the third column by random number from a CSV file:

if the value in the first column is 'A' I want a random number between (1 and 5). If the value is B I want a random number between (2 and 6) and if the value is C, and random number between (3 and 7).

import csv
import random
letters_randoms = {
    'A': [1, 5],
    'B': [2, 6],
    'C': [3, 7],
}
rows = [] #result
with open('file.csv', 'r', encoding='utf-8') as file:
    reader = csv.reader(file)
    rows.append(next(reader))  # Skip the first line (header)
    for row in reader:
        letter = row[0].upper()
        row[2] = random.randint(letters_randoms[letter]
                                [0], letters_randoms[letter][1])# or just *letters_randoms[letter]
        rows.append(row)
# modify csv file
with open('file.csv', 'w', newline='', encoding='utf-8') as file:
    writer = csv.writer(file)
    writer.writerows(rows)

Result:(file.csv)

LETTER,COLOR,Random Number
A,Green,3
c,Red,5
B,Red,2
B,Green,2
c,Blue,5
A,Purple,5
B,Green,3
A,Orange,3
c,Black,4
c,Red,5