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Dictionary sorting of ArrayList of Arraylist in java

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0

1

I want to sort the ArrayList of ArrayList<Integer>, which looks like.

ArrayList<ArrayList<Integer>> allres = new ArrayList<ArrayList<Integer>>();
Collections.sort(allres, new Comparator<ArrayList<Integer>>() 
 public int compare(ArrayList<Integer> a, ArrayList<Integer> b) 
 for (int i = 0; i < a.size(); i++) 
 if (a.get(i) < b.get(i)) 
 return -1;
 else if (a.get(i) == b.get(i)) 
 continue;
 else 
 return 1;
 
 
 return -1;
 
);

But for some input, it is not giving the result of dictionary sort.

java sorting arraylist

share|improve this question

edited Mar 23 at 12:06

Pshemo

96.9k15135194

asked Mar 23 at 9:57

Sujeet_JavaDevSujeet_JavaDev

61

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Yeah but, what's a dictionary sort? And what's the wanted output?
  
  – LppEdd
  Mar 23 at 10:01
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  the compare method never returns 0. what if all items are equal?
  
  – Sharon Ben Asher
  Mar 23 at 10:06
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The comparator is kinda weird. It compares two lists of integers by first found difference (ie list [1,6,2,3,8] would be smaller than [1,6,3,0,1]) because the the first difference is at index 2 and number 2 is smaller than 3 the rest is ignored. I don't know what is the meaning of such a comparison. There's possible IndexOutOfBoundsException if the first list is longer than the second and the items are equal. Another weird behaviour: the comparator consider first list "smaller" (returns -1) than the second in case they are the same...
  
  – bambula
  Mar 23 at 10:13
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @bambula This kind of comparators makes sense for version numbers and several other things. The concept is sound, it's just the implementation that's broken.
  
  – Roland Illig
  Mar 23 at 10:24
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  And what is "some input". Don't make us guess, provide us with details instead.
  
  – Roland Illig
  Mar 23 at 10:27
  

  
  
  
  

 | 
show 1 more comment

0

1

I want to sort the ArrayList of ArrayList<Integer>, which looks like.

ArrayList<ArrayList<Integer>> allres = new ArrayList<ArrayList<Integer>>();
Collections.sort(allres, new Comparator<ArrayList<Integer>>() 
 public int compare(ArrayList<Integer> a, ArrayList<Integer> b) 
 for (int i = 0; i < a.size(); i++) 
 if (a.get(i) < b.get(i)) 
 return -1;
 else if (a.get(i) == b.get(i)) 
 continue;
 else 
 return 1;
 
 
 return -1;
 
);

But for some input, it is not giving the result of dictionary sort.

java sorting arraylist

share|improve this question

edited Mar 23 at 12:06

Pshemo

96.9k15135194

asked Mar 23 at 9:57

Sujeet_JavaDevSujeet_JavaDev

61

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Yeah but, what's a dictionary sort? And what's the wanted output?
  
  – LppEdd
  Mar 23 at 10:01
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  the compare method never returns 0. what if all items are equal?
  
  – Sharon Ben Asher
  Mar 23 at 10:06
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  The comparator is kinda weird. It compares two lists of integers by first found difference (ie list [1,6,2,3,8] would be smaller than [1,6,3,0,1]) because the the first difference is at index 2 and number 2 is smaller than 3 the rest is ignored. I don't know what is the meaning of such a comparison. There's possible IndexOutOfBoundsException if the first list is longer than the second and the items are equal. Another weird behaviour: the comparator consider first list "smaller" (returns -1) than the second in case they are the same...
  
  – bambula
  Mar 23 at 10:13
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @bambula This kind of comparators makes sense for version numbers and several other things. The concept is sound, it's just the implementation that's broken.
  
  – Roland Illig
  Mar 23 at 10:24
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  And what is "some input". Don't make us guess, provide us with details instead.
  
  – Roland Illig
  Mar 23 at 10:27
  

  
  
  
  

 | 
show 1 more comment

I want to sort the ArrayList of ArrayList<Integer>, which looks like.

ArrayList<ArrayList<Integer>> allres = new ArrayList<ArrayList<Integer>>();
Collections.sort(allres, new Comparator<ArrayList<Integer>>() 
 public int compare(ArrayList<Integer> a, ArrayList<Integer> b) 
 for (int i = 0; i < a.size(); i++) 
 if (a.get(i) < b.get(i)) 
 return -1;
 else if (a.get(i) == b.get(i)) 
 continue;
 else 
 return 1;
 
 
 return -1;
 
);

But for some input, it is not giving the result of dictionary sort.

java sorting arraylist

share|improve this question

edited Mar 23 at 12:06

Pshemo

96.9k15135194

asked Mar 23 at 9:57

Sujeet_JavaDevSujeet_JavaDev

61

ArrayList<ArrayList<Integer>> allres = new ArrayList<ArrayList<Integer>>();
Collections.sort(allres, new Comparator<ArrayList<Integer>>() 
 public int compare(ArrayList<Integer> a, ArrayList<Integer> b) 
 for (int i = 0; i < a.size(); i++) 
 if (a.get(i) < b.get(i)) 
 return -1;
 else if (a.get(i) == b.get(i)) 
 continue;
 else 
 return 1;
 
 
 return -1;
 
);

share|improve this question

edited Mar 23 at 12:06

Pshemo

96.9k15135194

asked Mar 23 at 9:57

Sujeet_JavaDevSujeet_JavaDev

61

share|improve this question

edited Mar 23 at 12:06

Pshemo

96.9k15135194

asked Mar 23 at 9:57

Sujeet_JavaDevSujeet_JavaDev

61

edited Mar 23 at 12:06

Pshemo

96.9k15135194

edited Mar 23 at 12:06

Pshemo

96.9k15135194

asked Mar 23 at 9:57

Sujeet_JavaDevSujeet_JavaDev

61

asked Mar 23 at 9:57

Sujeet_JavaDevSujeet_JavaDev

61

1 Answer
1

active

oldest

votes

1

Comparator functions that contain 1 or -1 are error prone.

Instead, you should write it like this:

public static int lexicographically(List<Integer> a, List<Integer> b) 
 for (int i = 0, end = Math.min(a.size(), b.size()); i < end; i++) 
 int res = Integer.compare(a.get(i), b.get(i));
 if (res != 0)
 return res;
 
 return Integer.compare(a.size(), b.size());

This style of writing comparator functions prevents various common mistakes, such as never returning 0.

The most important pattern in this style is:

1. Compare by the first criterion.


2. If the given values differ, return the comparison result and be done.


3. Take the next criterion, continue with step 1.


4. If there are no criteria left, return 0.

share|improve this answer

edited Mar 23 at 10:30

answered Mar 23 at 10:20

Roland IlligRoland Illig

31.3k96493

add a comment | 

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1

Comparator functions that contain 1 or -1 are error prone.

Instead, you should write it like this:

public static int lexicographically(List<Integer> a, List<Integer> b) 
 for (int i = 0, end = Math.min(a.size(), b.size()); i < end; i++) 
 int res = Integer.compare(a.get(i), b.get(i));
 if (res != 0)
 return res;
 
 return Integer.compare(a.size(), b.size());

This style of writing comparator functions prevents various common mistakes, such as never returning 0.

The most important pattern in this style is:

1. Compare by the first criterion.


2. If the given values differ, return the comparison result and be done.


3. Take the next criterion, continue with step 1.


4. If there are no criteria left, return 0.

share|improve this answer

edited Mar 23 at 10:30

answered Mar 23 at 10:20

Roland IlligRoland Illig

31.3k96493

add a comment | 

1

Comparator functions that contain 1 or -1 are error prone.

Instead, you should write it like this:

public static int lexicographically(List<Integer> a, List<Integer> b) 
 for (int i = 0, end = Math.min(a.size(), b.size()); i < end; i++) 
 int res = Integer.compare(a.get(i), b.get(i));
 if (res != 0)
 return res;
 
 return Integer.compare(a.size(), b.size());

This style of writing comparator functions prevents various common mistakes, such as never returning 0.

The most important pattern in this style is:

1. Compare by the first criterion.


2. If the given values differ, return the comparison result and be done.


3. Take the next criterion, continue with step 1.


4. If there are no criteria left, return 0.

share|improve this answer

edited Mar 23 at 10:30

answered Mar 23 at 10:20

Roland IlligRoland Illig

31.3k96493

add a comment | 

Comparator functions that contain 1 or -1 are error prone.

Instead, you should write it like this:

public static int lexicographically(List<Integer> a, List<Integer> b) 
 for (int i = 0, end = Math.min(a.size(), b.size()); i < end; i++) 
 int res = Integer.compare(a.get(i), b.get(i));
 if (res != 0)
 return res;
 
 return Integer.compare(a.size(), b.size());

This style of writing comparator functions prevents various common mistakes, such as never returning 0.

The most important pattern in this style is:

1. Compare by the first criterion.


2. If the given values differ, return the comparison result and be done.


3. Take the next criterion, continue with step 1.


4. If there are no criteria left, return 0.

share|improve this answer

edited Mar 23 at 10:30

answered Mar 23 at 10:20

Roland IlligRoland Illig

31.3k96493

public static int lexicographically(List<Integer> a, List<Integer> b) 
 for (int i = 0, end = Math.min(a.size(), b.size()); i < end; i++) 
 int res = Integer.compare(a.get(i), b.get(i));
 if (res != 0)
 return res;
 
 return Integer.compare(a.size(), b.size());

share|improve this answer

edited Mar 23 at 10:30

answered Mar 23 at 10:20

Roland IlligRoland Illig

31.3k96493

answered Mar 23 at 10:20

Roland IlligRoland Illig

31.3k96493

answered Mar 23 at 10:20

Roland IlligRoland Illig

31.3k96493