Python: Populate lower triangle matrix from a list

Question

I have discrete-time data of airline ticket availability in csv format. This is used to represent ticket availability for a combination of departure and arrival time windows. Say my day is divided into 4 time periods -

12:01 AM to 6:00 AM, 
6:01 AM to 12:00 PM, 
12:01 PM to 6:00 PM,
6:01 PM to 12:00 AM

1 implies that the there are tickets available for that combination of departure and arrival, 0 otherwise. For this example, lets say that the ticket is available for all departure-arrival combinations, the csv file will have the following data:

1,1,1,1,1,1,1,1,1,1

This data is used to represent this matrix (please note that some of the combinations become zero here as they are illogical time combinations for a 24-hour period):

                    Departure time period           
                    12:01 AM to 6:00 AM | 6:01 AM to 12:00 PM  | 12:01 PM to 6:00 PM |  6:01 PM to 12:00 AM|
Arrival time period ------------------- | ---------------------|---------------------|---------------------|
12:01 AM to 6:00 AM                   1 |                     0|                    0|                    0|
6:01 AM to 12:00 PM                   1 |                     1|                    0|                    0|
12:01 PM to 6:00 PM                   1 |                     1|                    1|                    0|
6:01 PM to 12:00 AM                   1 |                     1|                    1|                    1|

The csv file has this data for multiple days. I have read in this data as a dictionary with the date being the key and the availability combinations as a list. The data processing is being done in Python 2.7. For a particular day I am now able to retrieve the list of availability by using the date key.

Now, I have 2 questions:

• How can I convert the data into the matrix type data structure. In essence this involves converting the list into a lower triangular matrix plus the diagonal elements. I have tried using the reshape function in numpy but that is not achieving this result.

• Once I have converted the matrix - I want to pictorially represent availability as a thematic grid - with all 1s as green squares and 0s as red squares. Is this achievable in Python? How?

I assumed that reading in the csv as a dictionary and then storing the availability elements in a list is the way to go as it seemed fairly straightforward. Modify the approach if you feel there are more clever ways to do this.

Any thoughts folks?!?

Answer 1

import numpy as np
import matplotlib.pyplot as plt

data = [1,1,1,1,1,1,1,1,1,1]
arr = np.zeros((4,4))
indices = np.tril_indices(4)
arr[indices] = data
print(arr)

# array([[ 1.,  0.,  0.,  0.],
#        [ 1.,  1.,  0.,  0.],
#        [ 1.,  1.,  1.,  0.],
#        [ 1.,  1.,  1.,  1.]])


plt.imshow(arr, interpolation='nearest', cmap=plt.get_cmap('RdYlGn'))
plt.show()

plots