Can I use python slicing to access one "column" of a nested tuple?

Question

I have a nested tuple that is basically a 2D table (returned from a MySQL query). Can I use slicing to get a list or tuple of one "column" of the table?

For example:

t = ((1,2,3),(3,4,5),(1,4,5),(9,8,7))

x = 6

How do I efficiently check whether x appears in the 3rd position of any of the tuples?

All the examples of slicing I can find only operate within a single tuple. I don't want to slice a "row" out of t. I want to slice it the other way -- vertically.

Solution 1

Your best bet here is to use a generator expression with the any() function:

if any(row[2] == x for row in t):
    # x appears in the third row of at least one tuple, do something

As far as using slicing to just get a column, here are a couple of options:

• Using zip():

  >>> zip(*t)[2]
  (3, 5, 5, 7)
  

• Using a list comprehension:

  >>> [row[2] for row in t]
  [3, 5, 5, 7]
  

Solution 2

I'll chime in with the numpy solution

import numpy
t = ((1,2,3),(3,4,5),(1,4,5),(9,8,7))
x = 6
col_id = 2

a = numpy.array(t)
print a[a[:,col_id] == x]