I have a list of lists:
>>> array = [["A","B","C"],["C","B","A"]]
I also have a key which I used enumerate to create:
>>> key = list(enumerate(["A","B","C"]))
>>> print (key)
[(0,"A"),(1,"B"),(2,"C")]
I want to use list comprehension to convert the strings in the array into numbers based on the key. I did the following and was able to get the result I wanted:
>>> for i in key:
... board = [[i[0] if x in i else x for x in y] for y in board]
>>> print(board)
[[0,1,2],[2,1,0]]
However, I can't seem to figure out how to use a single list comprehension without a for loop to obtain the result. Any ideas on how I would be able to do this?
If I understand you correctly, you want to convert the for-loop into list comprehension. You can create a mapped (in your question this is inverted key dictionary`) and then use list comprehension:
array = [["A","B","C"],["C","B","A"]]
mapper = {v:k for k, v in dict(enumerate(["A","B","C"])).items()}
print( [[mapper[v] for v in subl] for subl in array] )
Prints:
[[0, 1, 2], [2, 1, 0]]
EDIT: Thank to @kaya3, lighter version with just enumerate:
array = [["A","B","C"],["C","B","A"]]
mapper = {v:k for k, v in enumerate(["A","B","C"])}
print( [[mapper[v] for v in subl] for subl in array] )