# 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 code to demonstrate  ` `# initializing matrix ` `# using list comprehension ` ` `  `# Declaring rows ` `N ``=` `5` ` `  `# Declaring columns ` `M ``=` `4` ` `  `# using list comprehension  ` `# to initializing matrix ` `res ``=` `[ [ ``0` `for` `i ``in` `range``(N) ] ``for` `j ``in` `range``(M) ] ` ` `  `# printing result  ` `print``(``"The matrix after initializing : "` `+` `str``(res)) `

Output :

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 code to demonstrate  ` `# initializing matrix ` `# using list comprehension ` `# and * operator ` ` `  `# Declaring rows ` `N ``=` `5` ` `  `# Declaring columns ` `M ``=` `4` ` `  `# using list comprehension  ` `# to initializing matrix ` `res ``=` `[ [``0` `for` `i ``in` `range``(M)]] ``*` `N ` ` `  `# printing result  ` `print``(``"The matrix after initializing : "` `+` `str``(res)) `

Output :

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 code to demonstrate  ` `# initializing matrix ` `# * operator twice ` ` `  `# By: Pushpak Jalan, Tezpur University ` ` `  `# Declaring rows ` `N ``=` `5` ` `  `# Declaring columns ` `M ``=` `4` ` `  `# Using * operator twice to initialize matrix ` `res ``=` `[[``0``] ``*` `M] ``*` `N ` ` `  `# printing result  ` `print``(``"The matrix after initializing : "` `+` `str``(res)) `

Output :

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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Improved By : Pushpak_Jalan