Transform “list of tuples” into a flat list or a matrix

Question

With Sqlite, a \"select..from\" command returns the results \"output\", which prints (in python):

>>print output
[(12.2817, 12.2817), (0, 0), (8.52, 8.         


        

Answer 1

Update: Flattening using extend but without comprehension and without using list as iterator (fastest)

After checking the next answer to this that provided a faster solution via a list comprehension with dual for I did a little tweak and now it performs better, first the execution of list(...) was dragging a big percentage of time, then changing a list comprehension for a simple loop shaved a bit more as well.

The new solution is:

l = []
for row in output: l.extend(row)

---

Older:

Flattening with map/extend:

l = []
list(map(l.extend, output))

Flattening with list comprehension instead of map

l = []
list(l.extend(row) for row in output)

---

some timeits for new extend and the improvement gotten by just removing list(...) for [...]:

import timeit
t = timeit.timeit
o = "output=list(zip(range(1000000000), range(10000000))); l=[]"
steps_ext = "for row in output: l.extend(row)"
steps_ext_old = "list(l.extend(row) for row in output)"
steps_ext_remove_list = "[l.extend(row) for row in output]"
steps_com = "[item for sublist in output for item in sublist]"

print("new extend:      ", t(steps_ext, setup=o, number=10))
print("old extend w []: ", t(steps_ext_remove_list, setup=o, number=10))
print("comprehension:   ", t(steps_com, setup=o, number=10,))
print("old extend:      ", t(steps_ext_old, setup=o, number=10))

>>> new extend:       4.502427191007882
>>> old extend w []:  5.281140706967562
>>> comprehension:    5.54302118299529
>>> old extend:       6.840151469223201    

Answer 2

use itertools chain:

>>> import itertools
>>> list(itertools.chain.from_iterable([(12.2817, 12.2817), (0, 0), (8.52, 8.52)]))
[12.2817, 12.2817, 0, 0, 8.52, 8.52]

Answer 3

>>> flat_list = []
>>> nested_list = [(1, 2, 4), (0, 9)]
>>> for a_tuple in nested_list:
...     flat_list.extend(list(a_tuple))
... 
>>> flat_list
[1, 2, 4, 0, 9]
>>> 

you could easily move from list of tuple to single list as shown above.