如何使用python从csv文件格式中读取数据

Question

I want to read CSV file.

In the first column of.CSV file, I have a different variable (eg, N11, N12, N21, N22,..., N38). In the 3rd column, I have different values against each variable. The values in the 3rd column are randomly placed (Not in any sequence).

I want to get the minimum and maximum value against each variable (N11, N12...etc). For example, N11 minimum = 1573231694 and N11 Maximum = 1573231738 is given in example data.

In .csv file, each variable contains thousand of tuples as shown below:

I was trying the below code. Can anybody help me to modify the below code according to the above requirement?

import csv
with open('example.csv') as csvfile:
    readCSV = csv.reader(csvfile, delimiter=',')
    for row in readCSV:
        print(row[2])

Thank you.

Answer 1

Working sample

N11,12,123,123,0
N21,12,133,123,0
N12,12,143,123,0
N32,12,125,123,0
N11,12,121,123,0
N12,12,121,123,0
N11,12,122,123,0
N21,12,127,123,0
N32,12,183,123,0
N14,12,193,123,0

Assumption

• If the first columns only has one value it will be set as both the max and min

The code, commented with explanation

import csv

# Collect the pairs in a dict of lists where the first value is the minimum 
# and the second the max

min_max = dict() 

with open('example.csv') as csvfile:
    readCSV = csv.reader(csvfile, delimiter=',')

    for row in readCSV:

        # Check if the value already exists in the dict
        row_val = min_max.get(row[0]) 

        if row_val is not None:
            row_min = min_max[row[0]][0] # Get the min
            row_max = min_max[row[0]][1] # Get the max

            # Check against current value
            min_max[row[0]][0] = min(row[2], row_min) 
            min_max[row[0]][1] = max(row[2], row_max)   
        else:
            # If it doesn't exist update the dict
            min_max[row[0]] = [row[2], row[2]]

    print(min_max)

Output

{'N11': ['121', '123'], 'N21': ['127', '133'], 'N12': ['121', '143'], 'N32': ['125', '183'], 'N14': ['193', '193']}

Answer 2

I'd personally recommend you to use the pandas module.

You can easily create datastructures and easily manage databases. It is an open source library providing high-performance, easy-to-use data structures and data analysis tools for the Python programming language.

Check out the documentation for using pandas here: https://pandas.pydata.org/pandas-docs/stable/

And for this particular problem, you could just do:

import pandas as pd
dataframe = pd.read_csv("*File Path Here*")

This creates a custom pandas datastructure named 'dataframe' (choice completely up to you obviously) whose data can be easily and efficiently manipulated

Answer 3

df=pd.DataFrame({'col1':['N11','N12','N11','N14'],'col2':[1, 3, 5, 7],'col3':[11,13, 15, 17]})
print("N11 max=",df['col3'][df['col1']=='N11'].max())
print("N11 Min=",df['col3'][df['col1']=='N11'].min())

output: N11 max= 15 N11 Min= 11