加载 csv 文件中的所有行 - Python

Question

I want to load a csv file into python. The csv file contains grades for a random number of students and a random number of assignments.

I want python to delete the header and the first column (Name of student) and this is my code:

with open("testgrades.csv") as f:

ncols = len(f.readline().split(','))
nrows = sum(1 for row in f)
grades = np.loadtxt("testgrades.csv", delimiter=',', skiprows=1, usecols=range(1,ncols+1))
print(document1)

The code works for columns but can't handle if I add one or more rows in the csv file?

My CSV file:

csv

And output from Python:

Output

Answer 1

Your csv image looks like a messed up spread sheet image. It isn't a copy of the csv file itself, which is plain text. You should be able to copy-n-paste that text to your question.

The Output image is an array, with numbers that correspond to the first 6 rows of the csv image.

Your question is not clear. I'm guessing you added the last 2 rows to the spread sheet, and are having problems loading those into numpy . I don't see anything wrong with those numbers in the spread sheet image. But if you show the actual csv file content, we might identify the problem. Maybe you aren't actually writing those added rows to the csv file.

Your code sample, with corrected indentation is:

with open("testgrades.csv") as f:
    ncols = len(f.readline().split(','))
    nrows = sum(1 for row in f)
grades = np.loadtxt("testgrades.csv", delimiter=',', skiprows=1, usecols=range(1,ncols+1))
print(grades)

I can see using the ncols to determine the number of columns. The usecols parameter needs an explicit list of columns, not some sort of all-but-first . You could have also gotten that number from a plain loadtxt (or genfromtxt ).

But why calculate nrows ? You don't appear to use it. And it isn't needed in the loadtxt . genfromtxt allows a max_rows parameter if you need to limit the number of rows read.

Answer 2

Python has a special module for reading and writing CSV files Python CSV

Python 2

import csv
with open('testgrades.csv', 'rb') as f:

Python 3

import csv
with open('testgrades.csv', newline='') as f: