Loop through and add values to array via for loop

Morning, I am trying to add all my values of Distance and Speed to an array, so I can plot them with PLT. However, python is only appending 1 value, why? What am I doing wrong? Code and output below: ”’

import cv2
import matplotlib.pyplot as plt
import numpy as np
list=["spect2.png","spect3.png","spect4.png","spect5.png","spect6.png", 
"spect7.png","spect8.png","spect9.png","spect11.png"]
for i in range(len(list)):
    curr_list=list[i]
    print("This is the image name reading: " + curr_list)

    im = cv2.imread(curr_list)

    red = [0,0,255]

    X,Y = np.where(np.all(im==red,axis=2))
    try:
        Average_X=sum(Y)/len(Y)
    except ZeroDivisionError:
        print("Zero div, cant")
    print(Average_X)


    yellow=[0,242,255]

    X,Y=np.where(np.all(im==yellow,axis=2))
    try:
        Average_Y=sum(Y)/len(Y)
    except ZeroDivisionError:
         print("Zero div, cant")
    print(Average_Y)

    amount_shifted=(Average_Y-Average_X)/Average_X

    speed=amount_shifted*3000000

    Distance=speed/22

    print("Speed away from us: "+str(speed))

    print("Distance away from us in mpc: "+str(Distance))
    curr_dis=Distance
    curr_amo=speed
    amount_list=[Distance]
    amount_list.append(curr_dis)
    amount_list_shifted=[speed]
    amount_list_shifted.append(curr_amo)


fig, ax = plt.subplots(figsize=(10, 6))
print(amount_list)
print(amount_list_shifted)
ax.scatter(amount_list, amount_list_shifted)
plt.show()

output:

This is the image name reading: spect2.png
323.0
329.2345679012346
Speed away from us: 57906.20341703948
Distance away from us in mpc: 2632.1001553199767
This is the image name reading: spect3.png
361.0
361.0
Speed away from us: 0.0
Distance away from us in mpc: 0.0
This is the image name reading: spect4.png
304.0
Zero div, cant
361.0
Speed away from us: 562500.0
Distance away from us in mpc: 25568.18181818182
This is the image name reading: spect5.png
341.0
350.6666666666667
Speed away from us: 85043.98826979489
Distance away from us in mpc: 3865.6358304452224
This is the image name reading: spect6.png
407.0
411.0
Speed away from us: 29484.029484029485
Distance away from us in mpc: 1340.1831583649766
This is the image name reading: spect7.png
413.0
418.6441717791411
Speed away from us: 40998.82648286526
Distance away from us in mpc: 1863.583021948421
This is the image name reading: spect8.png
342.0
354.95454545454544
Speed away from us: 113636.36363636349
Distance away from us in mpc: 5165.28925619834
This is the image name reading: spect9.png
343.0
348.9032258064516
Speed away from us: 51631.71259287102
Distance away from us in mpc: 2346.896026948683
This is the image name reading: spect11.png
342.0
343.5409836065574
Speed away from us: 13517.400057521088
Distance away from us in mpc: 614.4272753418677
[614.4272753418677, 614.4272753418677]
[13517.400057521088, 13517.400057521088]

”’ AS you can see the array is ONLY showing Distance and same distance again, HOW do I get it to add all the Distance and Speed values?

Answer

In every loop iteration, you very specifically erase your previous list, and replace it with two copies of the current data. I’ll focus on only one variable:

curr_dis=Distance                # the two variables are now the same value
amount_list=[Distance]           # over-write amount_list with only the current value
amount_list.append(curr_dis)     # append another copy of the current value

You have two things to upgrade in your programming skills:

(1) Learn basic debugging. If nothing else, insert strategic print statements to display variables of interest, and to trace your program flow.

(2) Learn basic techniques with data structures. In this case, you need to repeat your tutorial materials on handling a sequence (string, list, tuple, etc.). To accumulate a list the basic pattern is

a = []
while ... :
    create a new_value for the list
    a.append(new_value)

print(a)

Can you finish from here?

Advertisement

Answer