Massing an array in python

Question

Suppose I have this simple array:

simple_list = [ ('1', 'a', 'aa'), ('2', 'b', 'bb'), ('3', 'c', 'cc') ] 

If we look at this list as a table where the columns are separated by lumps and rows separated by tuples, I want to create a function that retrieves only the columns that I want. for example, this function will look something like this:

 get_columns(array, tuple_columns_selector)) 

For example, I want to collect only the first and third columns from it, in this case it will return another array with new values ​​to me:

if:

 get_columns(simple_list, (0,2)) get_columns(simple_list, (0,)) 

it will return something like:

 [('1', 'aa'), ('2', 'bb'), ('1', 'cc')] [1, 2, 3] 

And so on. Could you help me create this get_columns function please? Here is the code I tried:

 def get_columns(arr, columns): result_list = [] for ii in arr: for i in columns: result_list.append(ii[i]) return result_list to_do_list = [ ('Wake Up', True), ('Brush Teeh', True), ('Go to work', True), ('Take a shower', True), ('Go to bed', False) ] print(get_columns(to_do_list, (0,))) 

Answer 1

Use the magic of operator.itemgetter and map :

 from operator import itemgetter simple_list = [ ('1', 'a', 'aa'), ('2', 'b', 'bb'), ('3', 'c', 'cc') ] cols = (1,) # can be (0, 2) fn = itemgetter(*cols) print map(fn, simple_list) 

Return:

 [('1', 'aa'), ('2', 'bb'), ('3', 'cc')] 

when cols is (0, 2) .

And it returns:

 [1,2,3] 

when cols (1,) .

So your get_columns function could be

 def get_columns(data, cols): return map(itemgetter(*cols), data) 

Answer 2

@Kopos answer looks good, I just wanted to share one without additional libraries.

 simple_list = [ ('1', 'a', 'aa'), ('2', 'b', 'bb'), ('3', 'c', 'cc') ] def get_columns(array, tuple_columns_selector): return [tuple(elem[i] for i in tuple_columns_selector) for elem in array] def get_columns_multiple_lines(array, tuple_columns_selector): # The only difference between the result of this version and the other is that this one returns a list of lists # while the other returns a list of tuples resulting_list = [] # Create the variable that will store the resulting list for elem in array: # Loop for each element in array resulting_list.append([]) # We add a new "empty row" to store all the columns needed for i in tuple_columns_selector: # Loop for each column needed resulting_list[-1].append(elem[i]) # We append the column value to the last item in resulting_list return resulting_list print get_columns(simple_list, (0,2)) # outputs [('1', 'aa'), ('2', 'bb'), ('3', 'cc')] print get_columns(simple_list, (0,)) # outputs [('1',), ('2',), ('3',)] print get_columns_multiple_lines(simple_list, (0,2)) # outputs [['1', 'aa'], ['2', 'bb'], ['3', 'cc']] 

The only difference is the return value when tuple_columns_selector is only one column. If this is an important difference, I can “fix” it, but you should think about how this value will be used, and if it is convenient for it to have different possible structures.