CODEWITHSUNDEEP
pythonarraysfor-loop
BHudson
BHudson

Reputation: 707

Random Path with Several Trajectories (for loop/array not right?)

I am trying to code a random path with several trajectories. My code is below and calculates a path, but the for loop does not create multiple different paths. Rather, it plots the same path n times on top of itself. I want to be a able to graph n number of different paths from within the same for loop, store the values in a single array, then graph them next to each other. Any idea what I am doing wrong?

from numpy.random import randint
n = 1000
moves = randint(0, 2, size=n)
y = 0
x = [y]
n2 = 5

for t in range(n2):
    for i in moves:
        if i == 1:
            y = y + 1
        if i == 0:
            y = y - 1
        x.append(y)
    plt.plot(x)
    y = 0
    x = [y]

Upvotes: 0

Views: 977

Answers (1)

javidcf
javidcf

Reputation: 59731

If you want to create a different path on each iteration of the loop then you should call randint inside of the loop, and calculate the path there

from numpy.random import randint
n = 1000
n2 = 5

for t in range(n2):
    moves = randint(0, 2, size=n)
    y = 0
    x = [y]
    for i in moves:
        if i == 1:
            y = y + 1
        if i == 0:
            y = y - 1
        x.append(y)
    plt.plot(x)
    y = 0
    x = [y]

If you want to store all the computed paths, you can store them in a list or array:

from numpy.random import randint
n = 1000
n2 = 5
paths = []  # use something like numpy.empty((n2, n)) to use an array

for t in range(n2):
    moves = randint(0, 2, size=n)
    y = 0
    x = [y]
    for i in moves:
        if i == 1:
            y = y + 1
        if i == 0:
            y = y - 1
        x.append(y)
    paths.append(x)  # use something like paths[t] = x with an array
    plt.plot(x)
    y = 0
    x = [y]

Then paths[i] would contain the i-th computed path, and paths[i][j] (or paths[i, j] with an array) the j-th position of the i-th path.

Yet another alternative would be to store all the paths in a linear list (or a one-dimensional array) one after the other, so paths[:n] would be the first path, then paths[n:2*n], paths[2*n:3*n], etc.

Upvotes: 2

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