Remove zero values from a Java HashMap

Question

I have a HashMap with float values.

HashMap<Integer,Float> map : {(1,0.0),(2,0.0),(3,2000.0),(4,3000.0)}

I want to remove all the entries in it with zero values. The result should be:

 map : {(3,2000.0),(4,3000.0)}

Update: I'm using Java 7

LuCio · Accepted Answer · 2018-11-23T07:56:06.410

6

As of Java 8 you can simply use

map.values().removeIf(f -> f == 0f);

According to the JavaDoc this will remove all of the elements of map that satisfy the given predicate.

EDIT
As you updated your question, that you are using Java 7 use an Iterator on the values():

Iterator<Float> iterator = map.values().iterator();
while (iterator.hasNext()) {
    if (iterator.next() == 0f) {
        iterator.remove();
    }
}

This works because according to the JavaDoc map.values()

Returns a Collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa.

edited Nov 23 '18 at 07:56

answered Nov 23 '18 at 07:22

LuCio

5,055
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Ya correct! But I'm using Java 7 in my Android studio. I have updated my question. – Sandeep Yohans Nov 23 '18 at 07:26
1

@SandeepYohans I've extended my answer. – LuCio Nov 23 '18 at 07:29
This code looks simpler than mine! Thanks! – Sandeep Yohans Nov 23 '18 at 07:44

score 0 · Answer 2 · answered Nov 23 '18 at 07:18

0

for (Iterator<Map.Entry<Integer,Float>> it = map.entrySet().iterator(); 
 it.hasNext();) 
 {
     Map.Entry<Integer, Float> entry = it.next();
     if (entry.getValue() == 0.0) {
        it.remove();
     }
   }

answered Nov 23 '18 at 07:18

Sandeep Yohans

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Oleg Cherednik · Answer 3 · 2018-11-23T08:05:44.287

0

Pay attention on compare not integer values. double and float should not be compared with ==. This should be a rule, because this is precise vlue, and == 0 should menas smth. like -10E-12 <= float <= 10E-12 (delta range).

// Java 7
Iterator<Float> it = map.values().iterator();

while (it.hasNext()) {
    if (it.next().compareTo(0f) == 0)
        it.remove();
}

// Java 8
map.values().removeIf(value -> Float.compare(value, 0) == 0);

edited Nov 23 '18 at 08:05

answered Nov 23 '18 at 07:35

Oleg Cherednik

17,377
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1

Or : `it.next().compareTo(0f)` – LuCio Nov 23 '18 at 07:55
No point calling Float.compare (or compareTo) as that simply implies `==`. It certainly doesn't use deltas. – DodgyCodeException Dec 29 '18 at 11:36

Remove zero values from a Java HashMap

3 Answers3