Creating a Run length for a number matrix in Python

Question

I’m trying to create a run length for this matrix (see below) in Python that prints the matrix to a list in the following format [84, 2, 90, 2, 88, 1...].

The matrix layout

84 84 90 90
88 93 93 93
93 93 93 93
87 87 87 94

I don't have a lot of experience with run length loops so any helpful suggestions would be appreciated.

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chickity china chinese chicken · Accepted Answer · 2018-11-15T23:46:31.747

One way might be to use the list count() method on each sublist in the matrix:

>>> m = [[84, 84, 90, 90],
...      [88, 93, 93, 93],
...      [93, 93, 93, 93],
...      [87, 87, 87, 94]]

>>> l = []
>>> for row in m:
...     for x in sorted(set(row)):
...         l.extend([x, row.count(x)])

Or if you prefer one-liners:

[l.extend([x, row.count(x)]) for row in m for x in sorted(set(row))]

Then,

>>> print(l)
[84, 2, 90, 2, 88, 1, 93, 3, 93, 4, 87, 3, 94, 1]

score 0 · Answer 2 · answered Nov 16 '18 at 00:41

The answer given by @davedwards is extremely elegant.

Here is the solution that I wrote, which has the same run-time as his solution on my machine.

def run_length_encoding(matrix):
    # List for storing run length encoding
    encoding = []

    # Counts the number of occurrences
    count = 0

    # Initialize previous element to first element in matrix
    previous_element = matrix[0][0]

    for row in matrix:
        for current_element in row:
            if current_element == previous_element:
                count += 1
            else:
                encoding.append(previous_element)
                encoding.append(count)

                # Reset counter and update previous element
                count = 1
                previous_element = current_element

    # Append last element since loop exited.
    encoding.append(previous_element)
    encoding.append(count)

    return encoding

score 0 · Answer 3 · answered Oct 29 '19 at 11:31

Using the high-performance pyrle library for run length arithmetic:

# pip install pyrle
# or
# conda install -c bioconda pyrle

from pyrle import Rle
data = [int(n) for n in "84 84 90 90 88 93 93 93 93 93 93 93 87 87 87 94".split()] 
rle = Rle(data)
rle
# +--------+------+------+------+------+------+------+
# | Runs   | 2    | 2    | 1    | 7    | 3    | 1    |
# |--------+------+------+------+------+------+------|
# | Values | 84.0 | 90.0 | 88.0 | 93.0 | 87.0 | 94.0 |
# +--------+------+------+------+------+------+------+
# Rle of length 16 containing 6 elements

rle + rle
# +--------+-------+-------+-------+-------+-------+-------+
# | Runs   | 2     | 2     | 1     | 7     | 3     | 1     |
# |--------+-------+-------+-------+-------+-------+-------|
# | Values | 168.0 | 180.0 | 176.0 | 186.0 | 174.0 | 188.0 |
# +--------+-------+-------+-------+-------+-------+-------+
# Rle of length 16 containing 6 elements

Creating a Run length for a number matrix in Python

3 Answers3