Count of elements in an array, storing information in another

Question

Count of elements in an array, storing information in another

Navigation

#1 by (1 votes)
#2 by (0 votes)

1

Hello, I'm a beginner in python and I'm doing an exercise that consists of reading all the numbers in an array and adding in another array the numbers in the previous one and how many times they appear. Consequently, matrix 2 will have two lines, one containing the numbers, and the second as many times as they appear. For example, if there is a number 10 and it appears 3 times, the second matrix will have the number 10 on the first line and the number 3 on the second line, both in the same column.

NOTE: Consider the first array as any one already declared.

...

matriz2=[]
linha1 = []
linha2 = []
qntde=0
linha1.append(0)
for l in range(numerodelinhas):
    for c in range(numerodecolunas):
        qntde = 0
        if(linha1.count(matriz[l][c])==0):
            if(l==0 and c == 0):
                linha1[0]=matriz[0][0]
            if(l != 0 or c != 0):
                linha1.append(matriz[l][c])
            for n in range(numerodelinhas):
                qntde = qntde + matriz[n].count(matriz[l][c])
            linha2.append(qntde)

matriz2.append(linha1)
matriz2.append(linha2)
cm2=0
for n in matriz2[0]:
    print (matriz2[0][cm2]," - ",matriz2[1][cm2])
    cm2+=1

The code worked, but it does not please me at all. Would you have a way to make it lean?

python matriz

asked by anonymous 05.09.2018 / 16:59

2 answers

Chat with notice notification in laravel C # - EF Core questions to create relational model

score 1 · Answer 1

You can take advantage of the class collections.Counter , which gets a iterable or mapping and counts elements. The only adjustment is to make the array a list, but this is easily resolved with the itertools.chain () .

Here is an example usage:

from itertools import chain
from collections import Counter

# Matrix 4x4 apenas para exemplo
matriz = [
    [2, 4, 6, 8],
    [1, 2, 3, 5],
    [1, 1, 10, 20],
    [1, 2, 4, 7],
]

contador = Counter(chain.from_iterable(matriz))

# printa o objeto Counter, sendo as chaves o elemento
# contado e os valores quantas vezes eles aparecem na matriz
print(contador)

Output:

Counter({
    1: 4,
    2: 3,
    4: 2,
    6: 1,
    8: 1,
    3: 1,
    5: 1,
    10: 1,
    20: 1,
    7: 1
})

Repl.it

edit : chain(*matriz) changed to chain.from_iterable(matriz) to keep loading the lazy array. (suggestion: @nosklo)

score 0 · Answer 2

It has a much easier way of dealing with arrays and arrays in python, which is to use a library called numpy. Example:

In [1]: import numpy as np

# matriz1 gerada aleatoriamente de números de 0 a 5 com tamanho 3x3
In [2]: matriz1 = np.random.randint(0, 5, size=(3,3))

In [3]: matriz1
Out[3]: 
array([[1, 2, 4],
       [3, 1, 1],
       [2, 4, 4]])

# retorna os elementos únicos e o número de vezes em que cada um aparece
In [4]: elementos, contagem = np.unique(matriz1, return_counts=True)


# empilha os dois arrays de forma vertical, elementos em cima e contagem embaixo
In [5]: matriz2 = np.vstack([elementos, contagem])

In [6]: matriz2
Out[6]: 
array([[1, 2, 3, 4],
       [3, 2, 1, 3]])

For more information and documentation: link . Numpy is the base library for anyone working with machine learning and data science. There are several tutorials available, worth checking out.