Initialize Matrix in Python
Sometimes in the world of competitive programming, we need to initialise the matrix, but we don’t wish to do it in a longer way using a loop. We need a shorthand for this. This type of problem is quite common in dynamic programming domain. Let’s discuss certain ways in which this can be done.
Method #1 : Using List comprehension
List comprehension can be treated as a shorthand for performing this particular operation. In list comprehension, we can initialise the inner list and then extend this logic to each row again using the list comprehension.
Python3
# Python3 code to demonstrate # initializing matrix# using list comprehension # Declaring rowsN = 5 # Declaring columnsM = 4 # using list comprehension # to initializing matrixres = [ [ 0 for i in range(M) ] for j in range(N) ] # printing result print("The matrix after initializing : " + str(res)) |
The matrix after initializing : [[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
Method #2 : Using list comprehension + “*” operator
This problem can also be simplified using the * operator which can slightly reduce the tedious way task is done and can simply use multiply operator to extent the initialization to all N rows.
Python3
# Python3 code to demonstrate # initializing matrix# using list comprehension# and * operator # Declaring rowsN = 5 # Declaring columnsM = 4 # using list comprehension # to initializing matrixres = [ [0 for i in range(M)]] * N # printing result print("The matrix after initializing : " + str(res)) |
The matrix after initializing : [[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
Method #3 : Using + “*” operator twice
Similar to above example we can also initialize the columns using “*” operator twice.
Python3
# Python3 code to demonstrate # initializing matrix# * operator twice # By: Pushpak Jalan, Tezpur University # Declaring rowsN = 5 # Declaring columnsM = 4 # Using * operator twice to initialize matrixres = [[0] * M] * N # printing result print("The matrix after initializing : " + str(res)) |
The matrix after initializing : [[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
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