Extract columns from a 2 dimentional table

Extract columns from a 2 dimentional table - Printable Version

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Extract columns from a 2 dimentional table - Leyo - Feb-22-2022

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

RE: Extract columns from a 2 dimentional table - DPaul - Feb-22-2022

Hi,
You are making it more difficult than necessary Smile

M has 3 rows
Each row has 4 columns
so: for row in M...
and every row [0] is the first col....etc.
Paul

RE: Extract columns from a 2 dimentional table - BashBedlam - Feb-22-2022

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))

RE: Extract columns from a 2 dimentional table - Leyo - Feb-22-2022

(Feb-22-2022, 04:06 PM)DPaul Wrote: 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 Smile

RE: Extract columns from a 2 dimentional table - Leyo - Feb-22-2022

(Feb-22-2022, 06:56 PM)BashBedlam Wrote: 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))