How to construct a numpy array to display square scheme

Question

I want to ask whether it is possible to create with numpy this scheme:

  1 2 3
1       1
2       2
3       3
  1 2 3

... and then with commands I will add '0' or '*' to empty columns with the help of those numbers,but it is needed to have empty columns in corners. If it is possible how should I write the code?

Answer 1

import numpy as np
n = 3 #number of elements (3 in your example)
a = np.array([[0] * (n + 2)] * (n + 2)) #creating zero-fill 2-d array
for i in range(len(a)):
    for j in range(len(a[i])):
        if i == 0 or i == len(a) - 1: #if we are on a border of array
            if j != 0 and j != len(a[i]) - 1: #but not in corners
                a[i][j] = j
        if j == 0 or j == len(a[i]) - 1:# if we are on a border of array
            if i != 0 and i != len(a) - 1: #but not in corners
                a[i][j] = i
print(a)

Answer 2

To construct the array in an efficient manner, using array indexing and no loops, you can use:

import numpy as np

a = np.full((5, 5), ' ')
v = np.array((' ', '1', '2', '3', ' '))

a[0, :] = v
a[-1, :] = v
a[:, 0] = v
a[:, -1] = v

Printing the output:

>>> for i in a:
>>>     print(' '.join(i))

  1 2 3  
1       1
2       2
3       3
  1 2 3  

Answer 3

Adapted @LightVillet's answer to be less complex:

import numpy as np
n = 3 #number of elements (3 in your example)
a = np.full((n+2, n+2), ' ') #creating ' '-fill 2-d array

for i in range(1,n+1):
    a[0,i] = i    #top edge
    a[n+2,i] = i  #bottom edge
    a[i,0] = i    #left edge
    a[i,n+2] = i  #right edge

print(a)

Complexity: O(n)

Answer 4

More complex and inefficient way,

import numpy as np
size = int(input("Please enter size of the Matrix : "))
empty = np.zeros([size,size])
numberCounter = 0
rowNumberCounter = 0
for rowCounter in range(size):
    empty[rowCounter][size-1] = 0
    for colCounter in range(size):
        if rowCounter == 0 and colCounter == 0:
            empty[rowCounter][colCounter] = 0
        if rowCounter == 0 and colCounter < size-1:
            empty[rowCounter][colCounter] = numberCounter
            numberCounter = numberCounter + 1
        if rowCounter == size-1 and colCounter != 0 and colCounter <size-1:
            numberCounter = numberCounter + 1
            empty[rowCounter][colCounter] = numberCounter

    if rowCounter !=0 and rowCounter < size-1:
        empty[rowCounter][0] = rowNumberCounter + 1
        empty[rowCounter][size-1] = rowNumberCounter + 1
        rowNumberCounter = rowNumberCounter + 1
    numberCounter = 0

print(empty)

pushButton = input('Push * to convert 0 to * :')
if pushButton == '*':
        empty_str = empty.astype(str)
        for rowCounter in range(size):
            for colCounter in range(size):
                if empty_str[rowCounter][colCounter] == '0.0':
                    empty_str[rowCounter][colCounter] = '*'

print(empty_str)

Output;

Please enter size of the Matrix : 5
[[0. 1. 2. 3. 0.]
 [1. 0. 0. 0. 1.]
 [2. 0. 0. 0. 2.]
 [3. 0. 0. 0. 3.]
 [0. 1. 2. 3. 0.]]
Push * to convert 0 to * :*
[['*' '1.0' '2.0' '3.0' '*']
 ['1.0' '*' '*' '*' '1.0']
 ['2.0' '*' '*' '*' '2.0']
 ['3.0' '*' '*' '*' '3.0']
 ['*' '1.0' '2.0' '3.0' '*']]