Find smallest element in arraylist

[Gary Goldsmith]

Hi everyone, could anyone here please explain to me how to search an arraylist and return the smallest element from it? I know I need to search through the arraylist and do a compareto on each element, but not sure how to write it.
[ March 06, 2007: Message edited by: big momma ]

[Svend Rost]

Hi there,

first of all: Take a look at the naming policy here on the ranch
( http://www.javaranch.com/name.jsp ). Baiscly you need a first and a
second name..

You need to do the following:

    
Initialize the integer 'current_lowest_value' with the value of an integers
maximal value.
 
for all elements in the list:
 - get the "current" element
 - compare the current element with the value of the current_lowest_value.
 - save the lowest value in current_lowest_value

Did that help ? if not, where are you stuck in your implementation?

/Svend Rost

[Gary Goldsmith]

I apologize about the naming problem (I think ive fixed it now).

As for my problem I 'think' I know how to do it algorithmically:
Get the first element in the array compare to the next one, if its smaller than the first one then make that 'i' and then compare that one to the next one in the array, and so forth until the smallest element is found which I can then pass to a method. But I'm a bit lost with the actual code.

[pete stein]

Why don't you show your attempt at coding it first and where your stuck. Or if you can't get code working, at least show pseudocode. You'll get much greater benefit to struggle with the problem first before seeing a solution.

[Gary Goldsmith]

 
private int j;
 
    for(int i=0; i < this.queue.size(); i++)
{
           //pseudocode
           // compare each element and find the smallest number
           if(element 0 <= element 1)
              {
                  temp = j;
              }
}
 

   

[Gary Goldsmith]

Maybe something like this would be better?

   
public int compare(Object arg0, Object arg1) {
for(int i=0; i < this.myArray.size(); i++)
{
//do something here
}
return 0;
}
 
 

[Svend Rost]

Hi John,

okay, so you know which steps to take when you have to solve this problem
but you have problems with the implementation.. let's take at what you wrote:

    
private int j;     
for(int i=0; i < this.queue.size(); i++)
  if(element 0 <= element 1)              
   {
                  temp = j;
    }
}

- Let's use j as the variable that contains the current lowest value. We need
to init it with a large value, say 10000 (you can take a look at the Interger, http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Integer.html ,
class for a nicer way to initialize j with another value than 10000).

- Your for-loop condition looks good, if queue is an array list you gets
its size with the .size() method, and if queue is an array you gets its
length with the instane variable 'length'

- You need to remove an element from the arraylist/array. This is done by
queue[index] for an array, and you can look here: http://java.sun.com/j2se/1.4.2/docs/api/java/util/ArrayList.html
for an approapriate method for the array list.

- The idea behind your comparision is also correct.. lets make it abit more
concrete:

if(new_value < j)
              {
                  j = new_value;
              }

Try to implement the above and post your results.. I'll check back later.

Happy coding

/Svend Rost

[Stan James]

Hmmm, we had a John Smith before ... is he gone? Does the ranch care about duplicate names?

[Svend Rost]

Originally posted by Stan James:
Hmmm, we had a John Smith before ... is he gone? Does the ranch care about duplicate names?

Although I havn't seen an official rule on this, this queryin the JavaRanch
forum gives the impression, that "no, the ranch doesn't".

/Svend Rost

[Gary Goldsmith]

Hi there again, well i tried doing the array part and couldn't get it, so I carried on with other things, but now I'm trying again.

    
        for (int i=0; i < myArray.size(); i++)
        {
           Test test1 = (Test)this.myArray.get(i);  
           // Test is a class with methods - such as getLength()     
        }
 

this I know gets me the last element in the arraylist.
test1.getLength() will get me the size of all the objects, I want to get the first element myArray.get(0) and then compare it to the next element.

ArrayList: 3, 5, 2, 9

I want to return the smallest element.

A pseudo style code answer would help very much
[ March 13, 2007: Message edited by: big momma ]

[Garrett Rowe]

Svend Rost gave a very appropriate pseudo-code example in his first post, was there a particular part of it that you didn't understand. Personally, I usually initialize the current_lowest_value to the first element in the collection, and then compare all the other elements to the current_lowest_value, updating it as necessary, but that is a trivial implementation detail.
[ March 13, 2007: Message edited by: Garrett Rowe ]

[Svend Rost]

Hi again,

to solve the problem of finding the smallest value in an array list you need
to solve the following steps (it is always a good idea to break your problems
into smaller steps, and them one by one):
- loop through an arraylist

- remove an element in the arraylist

- compare two of the elements in the list

- save the smallest of those two values

Lets make a skeleton system:

    
import java.util.ArrayList;
 
public class FindSmallestInteger
{
 public static void main(String[] args)
  {
   ArrayList myList = new ArrayList(); // make arrayList
   Integer smallestValue = new Integer(1000); //The smallest value
   Integer a = new Integer(1); // make test data
   Integer b = new Integer(4);
   Integer c = new Integer(7);
   myList.add(b); // insert element in arraylist
   myList.add(a);
   myList.add(c);
 
   //Loop through the array
   for ( ; ; ){
   //remove element from array list
 
   //compare with smallest value and save the smallest value
 
   }
 
   //Print the smallest value
   System.out.println("The smallest value is: "+smallestValue);
  }
}

Try to use the above.. and read my previous post.

/Svend Rost, who'll check back later

[Gary Goldsmith]

Thats been very helpful, thank you. I think i'm almost there. I shall work on it more tonight. So for now thank you, I will come back tomorrow with good or bad news