Comparing Two Arrays resulting into Third Array

Question

I have two Arrays:

firstArray=[['AF','AFGHANISTAN'],['AL','ALBANIA'],['DZ','ALGERIA'],['AS','AMERICAN SAMOA']]
secondArray=[[1,'AFGHANISTAN'],[3,'AMERICAN SAMOA']]

So I just need an Array which is like

thirdArray=[[1,'AF'],[3,'AS']]

I tried any(e[1] == firstArray[i][1] for e in secondArray) It returned me True and false if second element of both array matches. but i don't know how to build the third array.

Andrew Clark · Accepted Answer · 2012-10-22T18:21:52.923

First, convert firstArray into a dict with the country as the key and abbreviation as the value, then just look up the abbreviation for each country in secondArray using a list comprehension:

abbrevDict = {country: abbrev for abbrev, country in firstArray}
thirdArray = [[key, abbrevDict[country]] for key, country in secondArray]

If you are on a Python version without dict comprehensions (2.6 and below) you can use the following to create abbrevDict:

abbrevDict = dict((country, abbrev) for abbrev, country in firstArray)

Or the more concise but less readable:

abbrevDict = dict(map(reversed, firstArray))

score 2 · Answer 2 · answered Oct 22 '12 at 18:16

It is better to store them into dictionaries:

firstDictionary = {key:value for value, key in firstArray}
# in older versions of Python:
# firstDictionary = dict((key, value) for value, key in firstArray)

then you could get the 3rd array simply by dictionary look-up:

thirdArray = [[value, firstDictionary[key]] for value, key in secondArray]

score 2 · Answer 3 · answered Oct 22 '12 at 18:17

You could use an interim dict as a lookup:

firstArray=[['AF','AFGHANISTAN'],['AL','ALBANIA'],['DZ','ALGERIA'],['AS','AMERICAN SAMOA']]
secondArray=[[1,'AFGHANISTAN'],[3,'AMERICAN SAMOA']]

lookup = {snd:fst for fst, snd in firstArray}
thirdArray = [[n, lookup[name]] for n, name in secondArray]

score 0 · Answer 4 · answered Oct 22 '12 at 18:14

If a dictionary would do, there is a special purpose Counter dictionary for exactly this use case.

>>> from collections import Counter
>>> Counter(firstArray + secondArray)
Counter({['AF','AFGHANISTAN']: 1 ... })

Note that the arguments are reversed from what you requested, but that's easily remedied.

Ashwini Chaudhary · Answer 5 · 2012-10-22T18:22:24.793

0

use a list comprehension:

In [119]: fa=[['AF','AFGHANISTAN'],['AL','ALBANIA'],['DZ','ALGERIA'],['AS','AMERICAN SAMOA']]

In [120]: sa=[[1,'AFGHANISTAN'],[3,'AMERICAN SAMOA']]

In [121]: [[y[0],x[0]] for x in fa for y in sa if y[1]==x[1]]

Out[121]: [[1, 'AF'], [3, 'AS']]

edited Oct 22 '12 at 18:22

answered Oct 22 '12 at 18:15

Ashwini Chaudhary

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score 0 · Answer 6 · answered Oct 22 '12 at 18:18

The standard way to match data to a key is a dictionary. You can convert firstArray to a dictionary using dict comprehension.

firstDict = {x: y for (y, x) in firstArray}

You can then iterate over your second array using list comprehension.

[[i[0], firstDict[i[1]]] for i in secondArray]

Comparing Two Arrays resulting into Third Array

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