绘制/绘制此 csv 文件

Question

I'm completely new to Python and decided to learn it for our machine learning course as an engineer, however I'm having difficulties in retrieving values from my csv file which looks like the following:

Where I want to retrieve my B,C, and D values (retrieved from a Gravity sensor).

Code I've tried in my Jupyter Notebook:

import numpy as np    
import matplotlib.pyplot as plt
    
data_file = np.genfromtxt("Gravity.csv", delimiter="", names=["A","B","C","D"])
    
plt.plot(data_file['A'], data_file['B'],data_file['C'],data_file['D'])    
plt.show()

Answer 1

I converted your file to this format

A,B,C,D

0.1, 0.5, 0.1, 0.8

0.2, 0.1, 0.4, 0.1

0.1, 0.3, 0.1, 0.1 

and used the following code

import pandas as pd
values= pd.read_csv('./test.csv')

this works

Answer 2

I think your problem is that np.genfromtxt is also encoding the index column (values from 1 to 9) and also the header so that when you think you are selecting column 'B' you are actually selecting column A and so on.

this should work

import numpy as np    
import matplotlib.pyplot as plt
    
data_file = np.genfromtxt("Gravity.csv", delimiter=",", names=["index", "A","B","C","D"], skip_header=1)
    
plt.plot(data_file['B'],data_file['C'],data_file['D'])    
plt.show()

and a working example of the same concept but with artificial data

import pandas as pd
data = pd.DataFrame({'a':[1,2,3], 'b':[2,3,4], 'c':[4,5,6], 'd':[7,8,9]})
data.to_csv('./data.csv')
data2 = np.genfromtxt('./data.csv', delimiter=",", names=["index", "A","B","C","D"], skip_header=1)
plt.plot(data2['B'], data2['C'], data2['D'])
plt.show()

Answer 3

You have four columns in your data ( A , B , C , and D ) but you're only supplying three column names ( B , C , and D ). So it's linking name B to column A in the data and so on. Column D in the data is ignored like this so you need to designate four names so that each column can be queried as you expect.

Additionally, columnar data is handled well using pandas .

import pandas as pd
    
data_file = pd.read_csv("Gravity.csv", names = ['A', 'B', 'C', 'D'])