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Initialize Matrix in Python

• Last Updated : 30 Dec, 2020

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 rows``N ``=` `5`` ` `# Declaring columns``M ``=` `4`` ` `# using list comprehension ``# to initializing matrix``res ``=` `[ [ ``0` `for` `i ``in` `range``(M) ] ``for` `j ``in` `range``(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 #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 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

 `# 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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