Extract columns from a 2 dimentional table

[Leyo]

hello everyone,

I struggle on this exercise:
define a function col(mat, j) allowing to retrieve a column of the matrix. For example col(M, 1) will return [2, 6, 10].

here's the matrix (list of list created with loops):
M = [[1, 2, 3, 4],
[5, 6, 7, 8],
[9, 10, 11, 12]]

so far I wrote:

def col(mat,j):
    for i in range(3):  #search lines
        for j in range(4): #search columns
            return M[:][j] #return all elements from i column
col(0,1)

Output:
[1, 2, 3, 4]

I don't understand what to do with the parameter mat
can you help me understand what's wrong with my code?

I use Python 3 and Jupyter Notebook

Thanks in advance,
Leyo

Larz60+ write Feb-22-2022, 04:56 PM:
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[DPaul]

Hi,
You are making it more difficult than necessary
M has 3 rows
Each row has 4 columns
so: for row in M...
and every row [0] is the first col....etc.
Paul

[BashBedlam]

One reason for not using one and two letter variable names is that things likematcan be confusing. Descriptive variable names make the code much clearer and easier to work with and understand.

M = [[1, 2, 3, 4],
[5, 6, 7, 8],
[9, 10, 11, 12]]

def column (matrix, column_number) :
	output_column = []
	for row in matrix :
		output_column.append (row [column_number])
	return output_column

print (column (M, 1))

[Leyo]

Hi,
You are making it more difficult than necessary
M has 3 rows
Each row has 4 columns
so: for row in M...
and every row [0] is the first col....etc.
Paul

thanks Paul

[Leyo]

One reason for not using one and two letter variable names is that things likematcan be confusing. Descriptive variable names make the code much clearer and easier to work with and understand.

M = [[1, 2, 3, 4],
[5, 6, 7, 8],
[9, 10, 11, 12]]

def column (matrix, column_number) :
	output_column = []
	for row in matrix :
		output_column.append (row [column_number])
	return output_column

duly noted, thank you !

print (column (M, 1))