CODEWITHSUNDEEP
pythonmatplotlibplot
Vro
Vro

Reputation: 63

How would I plot points and make a line in python?

So Im supposed to plot graphs. Make a function plot_line(p1,p2) that takes two points as input arguments and plots the line between them. The two input arguments should be lists or tuples specifying x- and y-coordinates, i.e., p1 =(x1,y1)

I tried with this but my graph is just empty in the plot table. Nothing comes up

import matplotlib.pyplot as plt
    
print('this code will plot two points in a graph and make a line')

x1 = (float(input('enter first x value: ')))
y1 = (float(input('enter first y value: ')))
x2 = (float(input('enter second x value: ')))
y2 = (float(input('enter second y value: ')))


def plotline(p1,p2):
    p1=[x1,y1]
    p2=[x2,y2]
    
    return p1,p2


x=plotline(x1,x2)
y=plotline(x1,x2)

plt.plot(x,y, label='x,y')

plt.xlabel('x')
plt.ylabel('y')
plt.legend()
plt.axis([-10,10,-10,10])
plt.title('two lines')
plt.show()

Upvotes: 1

Views: 3618

Answers (2)

bench
bench

Reputation: 136

Complementing Prateek Tripathi and according to what I understood. There are two things you need to fix in your code.

Plotting

For more information on how to 'nicely' plot check matplotlib documentation

Your implementation

Your function plotline it's acting weird and and I think it doesn't do what it should. Try with this one

def plotLine(p1, p2):
    x = (p1[0], p2[0]) # Extracting x's values of points 
    y = (p1[1], p2[1]) # Extracting y's values of points
    plt.plot(x,y, '-o',label='x,y') # Plotting points

where p1 and p2 must be tuples of the coordinates corresponding to the points of your line. The tuples can be created manually by (x1, y1) and (x2, y2); or with a function similar the next one

def coordinates2tuple(x, y):
    return (x, y)

At the end

your code could looks like

import matplotlib.pyplot as plt

def coordinates2tuple(x, y):
    return (x, y)

def plotLine(p1, p2):
    x = (p1[0], p2[0]) # Extracting x's values of points 
    y = (p1[1], p2[1]) # Extracting y's values of points
    plt.plot(x,y, '-o',label='x,y') # Plotting points
    
    
    
print('this code will plot two points in a graph and make a line')

x1 = (float(input('enter first x value: ')))
y1 = (float(input('enter first y value: ')))
x2 = (float(input('enter second x value: ')))
y2 = (float(input('enter second y value: ')))



p1 = coordinates2tuple(x1, y1)
p2 = coordinates2tuple(x2, y2)

plotLine(p1, p2)

plt.xlabel('x')
plt.ylabel('y')
plt.legend()
plt.grid()
plt.axis([-10,10,-10,10])
plt.title('two lines')
plt.show()

That with the next execution

$ python3 trs.py 
this code will plot two points in a graph and make a line
enter first x value: 0
enter first y value: 0
enter second x value: 1
enter second y value: 1

shows enter image description here

Upvotes: 1

Prateek Tripathi
Prateek Tripathi

Reputation: 11

plt.plot() takes three input to work

If you just write plt.plot(3,4), it only pins the location but doesn't point it.

You need to write plt.plot(3,4,'o'). this way you will pin and point the location with a 'o' structure

Upvotes: 1

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