Comparing Two Arrays Resulting Into Third Array

I have two Arrays: firstArray=[['AF','AFGHANISTAN'],['AL','ALBANIA'],['DZ','ALGERIA'],['AS','AMERICAN SAMOA']] secondArray=[[1,'AFGHANISTAN'],[3,'AMERICAN SAMOA']] So I just need

Solution 1:

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))

Solution 2:

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]

Solution 3:

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]

Solution 4:

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.

Solution 5:

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]