How to cycle through colors in a plot for each iteration of a for loop

Question

I am trying to run a for loop that cycles through colours for each iteration of a for loop. I am finding similar questions that cycle through colours but not one that is dependent on a particular for loop. I provide some links below:

How to pick a new color for each plotted line within a figure in matplotlib?

matplotlib.cycler

Color cycler demo

My code is for a simple random walk

# Parameters
ntraj=10
n=20
p=0.4

# Initialize holder for trajectories
xtraj=np.zeros(n+1,float)

# Simulation
for j in range(ntraj):
    for i in range(n):
        xtraj[i+1]=xtraj[i]+2.0*np.random.binomial(1,p)-1.0

    plt.plot(range(n+1),xtraj,'b-',alpha=0.2)
plt.title("Simple Random Walk")  

I would like to create a line with a different colour for each j . I apologize if the answer is obvious. I am a novice at python.

Answer 1

As it is now, new colour will be taken for each line. If you want to limit choices and loop through a list you can use itertools.cycle :

from itertools import cycle

colours = cycle(['red', 'green', 'blue'])


# Simulation
for j in range(ntraj):
    for i in range(n):
        xtraj[i+1]=xtraj[i]+2.0*np.random.binomial(1,p)-1.0

    plt.plot(range(n+1),xtraj,'b-',alpha=0.2, color=colours.next())

Answer 2

I added a list of colors. I'm pretty sure they can be RGB or Hex. Then inside the j loop the color will switch to the next index.

colors = ['b','g','r','c','m','y']
# Parameters

# Simulation
for j in range(ntraj):
    color = colors[j % len(colors)]
    for i in range(n):
        xtraj[i+1]=xtraj[i]+2.0*np.random.binomial(1,p)-1.0

    plt.plot(range(n+1),xtraj,"{}-".format(color),alpha=0.2)
plt.title("Simple Random Walk")  

Answer 3

Choose any colour palette you like from matplotlib.cm

Try:

# Parameters
ntraj=10
n=20
p=0.4

colors = plt.cm.jet(np.linspace(0,1,ntraj))# Initialize holder for trajectories
xtraj=np.zeros(n+1,float)


# Simulation
for j in range(ntraj):
    for i in range(n):
        xtraj[i+1]=xtraj[i]+2.0*np.random.binomial(1,p)-1.0

    plt.plot(range(n+1),xtraj,'b-',alpha=0.2, color=colors[j])

plt.title("Simple Random Walk")

Answer 4

You have several options using matplotlib.pylplot.

Besides the already provided solutions, you can define your color directly and change the values depending on your for loop:

 # Parameters
ntraj=10
n=20
p=0.4

xtraj=np.zeros(n+1,float)


# Simulation
for j in range(ntraj):
    for i in range(n):
        xtraj[i+1]=xtraj[i]+2.0*np.random.binomial(1,p)-1.0

    ctemp = 0.1+(j-1)/ntraj
    plt.plot(range(n+1),xtraj,'b-',alpha=0.2, color=(ctemp, ctemp, ctemp))

plt.title("Simple Random Walk")