How to randomize two ArrayLists in the same fashion

Question

I have two arraylist filelist and imgList which related to each other  e g   H1 txt  related to  e1 jpg   How to automatically randomized the list of imgList according to the randomization of fileList  Like in excel  if we sort certain column  the other column will automatically follow   String    file     H1 txt   H2 txt   H3 txt   M4 txt   M5 txt   M6 txt    ArrayList lt String gt  fileList   new ArrayList lt String gt  Arrays asList file     String    img     e1 jpg   e2 jpg   e3 jpg   e4 jpg   e5 jpg   e6 jpg    ArrayList lt String gt  imgList   new ArrayList lt String gt  Arrays asList img       randomized files Collections shuffle fileList     output after randomization e g    fileList     M4 txt   M6 txt   H3 txt   M5 txt   H2 txt   H1 txt      intended output    imgList     e4 jpg   e6 jpg   e3 jpg   e5 jpg   e2 jpg   e1 jpg

User · Answer

You could do this with maps   Map lt String  String gt  fileToImg  List lt String gt  fileList   new ArrayList fileToImg keySet     Collections shuffle fileList   for String item  fileList        fileToImf get item       This will iterate through the images in the random order

User · Answer

Instead of having two arrays of Strings  have one array of a custom class which contains your two strings

User · Answer

Wrap them in another class so that you can end up with a single array or List of those objects   public class Data       private String txtFileName      private String imgFileName          Add generate c tor  getter setter  equals  hashCode and other boilerplate      Usage example   List lt Data gt  list   new ArrayList lt Data gt     list add new Data  H1 txt    e1 jpg     list add new Data  H2 txt    e2 jpg             Collections shuffle list

User · Answer

The simplest approach is to encapsulate the two values together into a type which has both the image and the file  Then build an ArrayList of that and shuffle it   That improves encapsulation as well  giving you the property that you ll always have the same number of files as images automatically   An alternative if you really don t like that idea would be to write the shuffle code yourself  there are plenty of examples of a modified Fisher-Yates shuffle in Java  including several on Stack Overflow I suspect  and just operate on both lists at the same time  But I d strongly recommend going with the  improve encapsulation  approach

User · Answer

Not totally sure what you mean by  automatically  - you can create a container object that holds both objects   public class FileImageHolder       String fileName      String imageName        TODO  insert stuff here    And then put that in an array list and randomize that array list   Otherwise  you would need to keep track of where each element moved in one list  and move it in the other one as well

User · Answer

Unless there s a way to retrieve the old index of the elements after they ve been shuffled  I d do it one of two ways   A     Make another list multi shuffler    0  1  2        file size    and shuffle it  Loop over it to get the order for your shuffled file image lists   ArrayList newFileList   new ArrayList    ArrayList newImgList   new ArrayList    for   i 0  i  or B     Make a StringWrapper class to hold the file image names and combine the two lists you ve already got into one  ArrayList combinedList

User · Answer

This can be done using the shuffle method    private List lt Integer gt  getJumbledList          List lt Integer gt  myArrayList2   new ArrayList lt Integer gt             myArrayList2 add 8           myArrayList2 add 4           myArrayList2 add 9           Collections shuffle myArrayList2           return myArrayList2

User · Answer

Use Collections shuffle   twice  with two Random objects initialized with the same seed   long seed   System nanoTime    Collections shuffle fileList  new Random seed    Collections shuffle imgList  new Random seed      Using two Random objects with the same seed ensures that both lists will be shuffled in exactly the same way   This allows for two separate collections

User · Answer

You can create an array containing the numbers 0 to 5 and shuffle those  Then use the result as a mapping of  oldIndex -  newIndex  and apply this mapping to both your original arrays

[java] How to randomize two ArrayLists in the same fashion?

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