How to remove null elements from multidimensional array in java

Question

I have an arrayList called Arr_SxCorrel_table2d like: The ArrayList is of the type: ArrayList<List<String>>

Arr_SxCorrel_table2dREMOVAL[[OF, RE, RE, RE, IND], [HA, 22, 3, 1, 4, 18%], [HA, 7, 3, 1, 4, 57%], [REG, 3, 1, 0, 1, 33%], [BING, 4, 3, 33, 32, 23%], [], [NOTE: details.], [], [], []]

I want to get rid of the elements that are empty. I tried:

for (int i=0;i<Arr_SxCorrel_table2d.size(); i++) {
                 if (Arr_SxCorrel_table2d.get(i) == null){
                     Arr_SxCorrel_table2d.remove(i); 
                         }
                 }

But nothing gets removed. Not sure what the next step should be

They can either be empty lists, or lists containing a single whitespace element. But you're obviously in a much better position to find out. — shmosel
– shmosel, Commented Apr 26, 2016 at 6:57
Could it contain a carriage return element. Is that possible so it would look as i does? — Sebastian Zeki
– Sebastian Zeki, Commented Apr 26, 2016 at 7:07

Eran · Accepted Answer · 2016-04-26 06:49:15Z

2

Your code removes null references from the outer List, it doesn't remove empty Lists.

Try :

for (int i=0;i<Arr_SxCorrel_table2d.size(); i++) {
    if (Arr_SxCorrel_table2d.get(i) == null || Arr_SxCorrel_table2d.get(i).isEmpty()){
        Arr_SxCorrel_table2d.remove(i); 
        i--;
    }
}

Note that i must be decremented whenever you remove an element from the List, since the indices of the elements that follow the removed element are decremented.

answered Apr 26, 2016 at 6:49

Eran

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2 Comments

Sebastian Zeki Over a year ago

OK but the elements are still not removed.

Eran Over a year ago

@SebastianZeki If the [] elements in the question represent empty inner Lists, they should be caught by the Arr_SxCorrel_table2d.get(i).isEmpty() condition and removed.

JanLeeYu · Accepted Answer · 2016-04-26 07:55:41Z

0

You can check their size if they are more than 0 :

for (int i = 0; i < Arr_SxCorrel_table2d.size(); i++) {
    if (Arr_SxCorrel_table2d.get(i).size() == 0) {
        Arr_SxCorrel_table2d.remove(i--);
    }
}

There's no need to check if there is a null value because it will not compile if the variable is given a null value.

answered Apr 26, 2016 at 7:55

JanLeeYu

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