Saturday, March 16, 2013

ZIP in python with examples

"""This(zip) builtin function returns a list of tuples"""
print "\nz will be a list:",z

print "\nExample 1:zip(string,list)"
for i in zip("Ajay kumar",[0,1,2,3,4,5,6,7,8,9]):
 print i,
print "\nExample 2:zip(list,list)"
for i in zip([1,2,3],[4,5,6]):
 print i,
print "\n Example 3:zip(tuple,tuple)"
for i in zip((1,2,3),('a','b','c')):
 print i,


z will be a list: [(1, 4), (2, 5), (3, 6)]

Example 1:zip(string,list)
('A', 0) ('j', 1) ('a', 2) ('y', 3) (' ', 4) ('k', 5) ('u', 6) ('m', 7) ('a', 8) ('r', 9) 
Example 2:zip(list,list)
(1, 4) (2, 5) (3, 6) 
 Example 3:zip(tuple,tuple)
(1, 'a') (2, 'b') (3, 'c')

Output can be seen in the image

One More version from some online book:
z = zip(list1, list2)
newlist1, newlist2 = zip(*z)

This works becauses the * syntax unpacks a list of values. The above code zips and unzips two lists, which is pointless, but the same syntax can be used to convert from a list of columns of data to a list of rows of data. For example, the following list comprehension reads in a file of tab-delimited data as a list of rows, where each row is a tuple of values:
rows = [line.rstrip().split('\t') for line in file(filename)]
If you want to flip the data through 90 degrees (i.e. convert from rows or data to columns of data), then you use:
columns = zip(*rows)
For example, if the data was originally (a, 1), (b, 2), (c, 3), it becomes (a, b, c), (1, 2, 3).
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