python map dictionary to array

Question

I have a list of data of the form:

[line1,a]
[line2,c]
[line3,b]

I want to use a mapping of a=5, c=15, b=10:

[line1,5]
[line2,15]
[line3,10]

I am trying to use this code, which I know is incorrect, can someone guide me on how to best achieve this:

mapping = {"a": 5, "b": 10, "c": 15}
applyMap = [line[1] = 'a' for line in data]

Thanks

EDIT: Just to clarify here, for one line, however I want this mapping to occur to all lines in the file:

Input: ["line1","a"]

Output: ["line1",5]

Please see my example, perhaps I was unclear, the first form where the array is (string,string) to become the second 'mapped' form of (string,int) — user1220022
– user1220022, Commented Mar 27, 2012 at 9:00

Cédric Julien · Accepted Answer · 2012-03-27 09:11:57Z

3

You could try with a list comprehension.

lines = [
   ["line1", "much_more_items1", "a"],
   ["line2", "much_more_items2", "c"],
   ["line3", "much_more_items3", "b"],
]
mapping = {"a": 5, "b": 10, "c": 15}
# here I assume the key you need to remove is at last position of your items
result = [ line[0:-1] + [mapping[line[-1]] for line in lines ]

edited Mar 27, 2012 at 9:11

answered Mar 27, 2012 at 9:03

Cédric Julien

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3 Comments

user1220022 Over a year ago

Is there a way to do this without specifying the x? My actual data has many more columns - I simplified it to make my explanation more clear.

Cédric Julien Over a year ago

@user1220022 : I updated my answer for the case you don't have only 2 members in your list items

user1220022 Over a year ago

This is exactly what I was after, I forgot about list iterations. Thanks!

Reto Aebersold · Accepted Answer · 2012-03-27 09:07:06Z

1

Try something like this:

data = [
    ['line1', 'a'],
    ['line2', 'c'],
    ['line3', 'b'],
]

mapping = {"a": 5, "b": 10, "c": 15}

applyMap = [[line[0], mapping[line[1]]] for line in data]

print applyMap

answered Mar 27, 2012 at 9:07

Reto Aebersold

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Comments

Dogbert · Accepted Answer · 2012-03-27 09:03:51Z

0

>>> data = [["line1", "a"], ["line2", "b"], ["line3", "c"]]
>>> mapping = { "a": 5, "b": 10, "c": 15}
>>> [[line[0], mapping[line[1]]] for line in data]
[['line1', 5], ['line2', 10], ['line3', 15]]

answered Mar 27, 2012 at 9:03

Dogbert

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5 Comments

user1220022 Over a year ago

Similarly, is there a way to do this without specifying the columns number? My actual data has many more columns - I simplified it to make my explanation more clear

Dogbert Over a year ago

@user1220022 Could you post the complete input / output you want in your question?

user1220022 Over a year ago

This output is 100% correct, however in my actual data I have 15 columns. So I don't want to do: [[line[0], mapping[line[1]], line[2],line[3]...,line[14],line[15]] for line in data]

Dogbert Over a year ago

You don't have to do that, as long as data is an array, it'll be completely iterated over.

user1220022 Over a year ago

So I only need to handle the columns before the mapping? ie your example code and the other columns will fill in on their own?

liupeixin · Accepted Answer · 2012-03-27 09:18:14Z

0

lineMap = {'line1': 'a', 'line2': 'b', 'line3': 'c'}  
cha2num = {'a': 5, 'b': 10, 'c': 15}  
result = [[key,cha2num[lineMap[key]]] for key in lineMap]  
print result

what you need is a map to relevance 'a' -> 5

answered Mar 27, 2012 at 9:18

liupeixin

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