How to compare current value with previous value in a loop

pallone · July 7th, 2011, 09:04 AM

Hi,

How do I compare the current value with previous value in a loop in javascript and determine if they are different?

The code below is my trial but to no avail. I am not comparing with the previous value, I am comparing only with the first value and this does not work for me. I must compare the values.

I would appreciate some help.

Cheers

Suppose I have a collection like this:

foo, foo, baz, foo

var firstName = names[0].value

for(var i =0; i < names.length; i++)
{
currentName = names[i].Value;
if(firstName != currentName)
{
textbox.disabled = true;
break;
}
}

Imar · July 7th, 2011, 09:07 AM

You need to update the previous value inside the loop as well. E.g.:

Code:

 
for(var i =0; i < names.length; i++)
{ 
  currentName = names[i].Value; 
  if(firstName != currentName)
  {
    textbox.disabled = true;
    break;
  }
  firstName = names[i].Value;
}

Hope this helps,

Imar

pallone · July 7th, 2011, 09:11 AM

Hi Imar,

thanks for the reply. I will try that.

pallone · July 7th, 2011, 09:16 AM

Hi Imar,

1 - But what happnes to firstName? You have not assigned it to any value? Do I still need to have my variable at the top ( var firstName = selectedNodes[0].value)

2 - Please could explain to me how this works?

for(var i =0; i < names.length; i++)
{
currentName = names[i].Value;
if(firstName != currentName)
{
textbox.disabled = true;
break;
}
firstName = names[i].Value;
}

Cheers

C

Imar · July 7th, 2011, 09:55 AM

Quote:

Do I still need to have my variable at the top ( var firstName = selectedNodes[0].value)

You'll need to assign it an empty value. This way there is no previous value. By renaming firstName to previous value, things may become clearer:

Code:

 
var previousValue = ''; 
for(var i =0; i < names.length; i++)
{ 
  currentName = names[i].Value; 
  if(previousValue != currentName) // Will be true on the first hit as previousValue == ''. Not sure if this is what you want
  {
    textbox.disabled = true;
    break;
  }
  previousValue = names[i].Value; // Assign previousValue the current value. In the next iteration of the loop, this means the previous value
}

Hope this helps,

Imar

pallone · July 7th, 2011, 10:14 AM

Hi Imar,

the previousValue cannot be an empty string otherwise it will be true and I will break out of the loop.

In my collection I have foo, foo,bar.foo. Therefore, if I compare the first value with the second then the condition is false because firts value == second value.

Then when I compare the second value with third value the condition will be true since second value != third value and I get out of the loop.

This is what I am trying to achive. If all the items in the collection are the same then nothing happens but if at least one is different then I have to detect it and get out.

pallone · July 7th, 2011, 10:37 AM

Hi Imar,

I think your first suggestion is going to work. I am comparing two values instead of one. What do you think?

Cheers

var selectedNodes = getNodeSet(xmlResult.xml, xmlResult.xml.documentElement,"//Insertion[@selected='true']/OrderNumber")

var firstSigName = selectedNodes[0].getAttribute("SignerName")

var firstIssueDate = getNode(xmlResult.xml, selectedNodes[0].parentNode, "Issue/@date")

for(var i =0; i < selectedNodes.length; i++)
{
var currentIssueDate = getNode(xmlResult.xml, selectedNodes[i].parentNode, "Issue/@date")
currSigName = selectedNodes[i].getAttribute("SignerName")

if(firstIssueDate.nodeValue != currentIssueDate.nodeValue && firstSigName != currSigName)
{
break;
}
firstSigName = selectedNodes[i].getAttribute("SignerName");
firstIssueDate = currentIssueDate;
}

Imar · July 7th, 2011, 05:56 PM

Many ways to Rome. If it works, it works ;-)

But if you're only looking for identical values, there's no need to keep track of the previous value. You can assign the first element to a variable, and then loop from the second element to the last, and compare them with the first. I think you had that in your first example, but you said that didn't work. However, this:

Quote:

If all the items in the collection are the same then nothing happens but if at least one is different then I have to detect it and get out.

seems to suggested this were what you're looking for....

This works for me and breaks out on the baz value:

Code:

 
    var names = 'foo,foo,baz,foo'.split(',');
    function Test(names)
    {
      var firstName = names[0];
      for (var i = 0; i < names.length; i++)
      {
        currentName = names[i];
        if (firstName != currentName)
        {
          textbox.disabled = true;
          break;
        }
      }
    }
    Test(names);

Hope this helps,

Imar

pallone · July 8th, 2011, 05:13 AM

Imar,

Thanks for all your help