Two dimensional array in python

Question

I want to know how to declare a two dimensional array in Python.

arr = [[]]

arr[0].append(\"aa1\")
arr[0].append(\"aa2\")
arr[1].append(\"bb1\")
arr[1].appe         


        

Answer 1

There aren't multidimensional arrays as such in Python, what you have is a list containing other lists.

>>> arr = [[]]
>>> len(arr)
1

What you have done is declare a list containing a single list. So arr[0] contains a list but arr[1] is not defined.

You can define a list containing two lists as follows:

arr = [[],[]]

Or to define a longer list you could use:

>>> arr = [[] for _ in range(5)]
>>> arr
[[], [], [], [], []]

What you shouldn't do is this:

arr = [[]] * 3

As this puts the same list in all three places in the container list:

>>> arr[0].append('test')
>>> arr
[['test'], ['test'], ['test']]

Answer 2

For compititve programming

1) For input the value in an 2D-Array

row=input()
main_list=[]
for i in range(0,row):
    temp_list=map(int,raw_input().split(" "))
    main_list.append(temp_list)

2) For displaying 2D Array

for i in range(0,row):
    for j in range(0,len(main_list[0]):
        print main_list[i][j],
        print

Answer 3

You do not "declare" arrays or anything else in python. You simply assign to a (new) variable. If you want a multidimensional array, simply add a new array as an array element.

arr = []
arr.append([])
arr[0].append('aa1')
arr[0].append('aa2')

or

arr = []
arr.append(['aa1', 'aa2'])

Answer 4

You try to append to second element in array, but it does not exist. Create it.

arr = [[]]

arr[0].append("aa1")
arr[0].append("aa2")
arr.append([])
arr[1].append("bb1")
arr[1].append("bb2")
arr[1].append("bb3")

Answer 5

x=3#rows
y=3#columns
a=[]#create an empty list first
for i in range(x):
    a.append([0]*y)#And again append empty lists to original list
    for j in range(y):
         a[i][j]=input("Enter the value")

Answer 6

You can first append elements to the initialized array and then for convenience, you can convert it into a numpy array.

import numpy as np
a = [] # declare null array
a.append(['aa1']) # append elements
a.append(['aa2'])
a.append(['aa3'])
print(a)
a_np = np.asarray(a) # convert to numpy array
print(a_np)