Convert List Object[] to MultiMap

Question

I have a query which returns List of Object[2]. I would like to convert this into a MultiMap which would contain Object[0] as key and Object[1] as value.

input list contains:

<id1, value1>
<id1, value2>
<id1, value3>
<id2, value1>
<id2, value2>
<id3, value2>

So when I do Collection coll = (Collection) multimap.get(id1);

col1 Should give --> value1,value2,value3

I can achive this looping through the list and putting it to the multimap, I would like to avoid that as my List is huge.

Thanks in advance!

not really anyway around looping that i can see. At most you'll find some library that loops for you. — Taylor
– Taylor, Commented Nov 13, 2013 at 22:16
"I would like to avoid that as my List is huge." This doesn't make sense - you can't punt all items from collection A to collection B without iterating over collection A. — millimoose
– millimoose, Commented Nov 13, 2013 at 22:18
You will have to loop through it. Also, measure before making assumptions. 'Huge' is quite relative and the time spent in putting the values in the multimap might be a few nano seconds only... — shutefan
– shutefan, Commented Nov 13, 2013 at 22:19
Addendum: if you use the MultiHashMap remember to preinitialize the multimap with the number of expected values in order to avoid unnecessary rehashing. — shutefan
– shutefan, Commented Nov 13, 2013 at 22:21

Jamil Seaidoun · Accepted Answer · 2013-11-13 22:15:24Z

2

for(Object obj[] : list ){
    multimap.put(obj[0], obj[1]);
}

Assuming youre using apache multimap

answered Nov 13, 2013 at 22:15

Jamil Seaidoun

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5 Comments

Gayathri Over a year ago

I would like to use something where I don't have to loop through.

millimoose Over a year ago

@Gayathri No such thing exists.

Dani Over a year ago

A matter of style, but I find clearer for begginers Object[] obj rather than Object obj[]

millimoose Over a year ago

@Darkhogg Clearer for anyone really. The latter is a C artefact, the former notation makes more sense given Java's type model.

Jamil Seaidoun Over a year ago

Sorry, im more used to C Conventions and it shows in my java code

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