Unable to Reverse an Integer Array

Question

I am currently creating a Legend component that maps text onto a gradient-looking legend that looks like this:

enter image description here

The central piece of code looks like the below (omitting the graphics declaration code snippets, as that's not the main piece):

        int numberOfItems = 10;
        int increment = (int) Math.Round((max - min), 0);
        int step = increment / numberOfItems;

Array that stores the step into an integer array the size of 10.

        int[] legend = new int[numberOfItems];
        for (int i = 0; i < legend.Length; i++) {
            legend[i] = step * i;
        }

String Reversal Code Snippet

        for (int i = (legend.Length - 1); i >= 0; i--) {
            g.DrawString(legend[i].ToString(), drawFontX, Brushes.White, ((newWidth / 2) - 5), (newHeight / 10) + (verticalDistance * i), stringFormatTimes);
        }

I have also tried:

        legend.Reverse();
        for (int i = 0; i < numberOfItems; i++) {
            g.DrawString(legend[i].ToString(), drawFontX, Brushes.White, ((newWidth / 2) - 5), (newHeight / 10) + (verticalDistance * i), stringFormatTimes);    
        }

As you can tell, I am trying to have the graph render the text from the largest value to the lowest, instead of what it is doing now, which is 0 - 1080.

My issue is, despite using both array reversal methods, I have been unable to reverse the legend array. I'm not quite sure what I am doing wrong.

usr · Accepted Answer · 2014-01-13 17:05:19Z

3

legend.Reverse binds to Enumerable.Reverse which returns you a copy. This should teach you not to mutate state if you don't have to. Instead, create new data from old data.

var legendContents =
 Enumerable.Range(0, numberOfItems)
 .Select(i => step * i)
 .Reverse()
 .Select(i => new { Text = i.ToString(), Y = (newHeight / 10) + (verticalDistance * i) }
 .ToArray();

//at this point you can easily examine all draw operations in the debugger

var xPos = ((newWidth / 2) - 5);
foreach (var legendItem in legendContents)
 g.DrawString(legendItem.Text, drawFontX, Brushes.White, xPos, legendItem.Y, stringFormatTimes);

Use a functional programming style. Much code saved, very readable now and easy to change.

answered Jan 13, 2014 at 17:05

usr

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4 Comments

theGreenCabbage Over a year ago

Are there any benefits to your solution and the ones Dan and Dave Bish suggested?

usr Over a year ago

There are multiple Reverse methods in the framework. Which one is picked depends on the exact type of the receiver. You might accidentally call List.Reverse for example. This is a design flaw in the BCL.

theGreenCabbage Over a year ago

Excuse me but did you look at my previous question's code snippets to implement the things below the array reversal =P?

theGreenCabbage Over a year ago

That's rather funny actually, unless I'm not in on the joke. I also named my items xPos and stringFormatTimes. Anyways - thanks for the help!

Dave Bish · Accepted Answer · 2014-01-13 17:05:22Z

2

You missed your assignment:

legend = legend.Reverse().ToArray();

answered Jan 13, 2014 at 17:05

Dave Bish

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Comments

Dan · Accepted Answer · 2014-01-13 17:11:13Z

2

Try this:

legend = legend.Reverse().ToArray();

The problem is that the Reverse method you are using doesn't change the original object; it creates a new object with the items from the original in reverse order. But you weren't saving the result of the Reverse method. It was just being ignored. If you reassign the value of the legend variable to the result of the Reverse method, this should fix your problem.

Another option would be to use a List<int>:

List<int> legend = new List<int>(numberOfItems);
for (int i = 0; i < numberOfItems; i++) {
    legend.Add(step * i);
}

//...

legend.Reverse();

Here you would be calling the Reverse method on the List<T> class which does change the order of the calling list instead of returning a new instance.

edited Jan 13, 2014 at 17:11

answered Jan 13, 2014 at 17:04

Dan

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