sorting array data

[dondigital]

I'm trying to figure out the best approach to grab data from an array. So heres the deal. I have byte array called curveData[256] filled will hex bytes that I've downloaded from a unit under test. Basically, I am trying to loop through this array of 256 bytes. I want to grab the 1st byte (of a 4 byte chunk), so [0], then [4] [8] and so on…so every 4th byte starting with the first and throwing them into the rpmArray. Then I want to grab the bytes in between, [1][2][3] …etc, and throw them into another array called multOffArray. Here is my code below

|0|1|2|3|4|5|6|7|…………|252|253|254|255|


int i;
byte[] rpmArray = new byte[64];
byte[] multOffArray = new byte[192];
for (i = 0; i < curveData.Length; i++ )
{
if (i%4 == 0 || i%4 == 4)
Array.Copy(curveData, curveData[i], rpmArray, curveData[i], 1);
else
Array.Copy(curveData, curveData[i], multOffArray, curveData[i+1], 3);
}
DisplayData(MessageType.Outgoing, "\n rpmArray: " + rpmArray);
DisplayData(MessageType.Outgoing, "\n multOffArray: " + multOffArray);

I'm getting errors saying that the index is out of bounds. When I check the bytes in the arrays where I’m storing this info, its not in the order that I anticipated and I am missing data. I tried to set it up so that at every index which is a multiple of 4, would initiate copying of data from the source array to my destination array. Maybe somebody can help me get this loop right. It's been a while since I've written code and I know this isn't right. If someone can help it'd be much appreciated.

[balabaster]

Would something like this be suitable?

System.Collections.ArrayList rpmArray = new  System.Collections.ArrayList();
System.Collections.ArrayList multOffArray = new System.Collections.ArrayList();
 
for (int i = 0; i < curveData.Length; i++)
{
    if (i % 4 == 0)
        rpmArray.Add(curveData[i]);
    else
        multOffArray.Add(curveData[i]);
}

It bypasses the need for array management and if you want to treat the ArrayLists as arrays, just reference them by rpmArray.ToArray() and multOffArray.ToArray()

[balabaster]

Or you could use the snazzy new LINQ to query the data set rather than iterating through it:

int rowIndex = 0;
 
var rpmQry = 
  from item in (
    from value in curveData 
    select new {index = rowIndex++, value}
  )
  where item.index % 4 == 0
  select item.value;
 
var rpmData = rpmQry.ToArray();

I tried to figure out a more succinct way of getting at the row indexes of each item to query for mod 4, but it's late and I'm tired... it would be nicer as a simple query rather than nested query. I started off with two queries, but I didn't like that it was being visited twice, until I wanted to reference it a second time for the multOffArray:

int rowIndex = 0;
var allDataQry = from item in curveData select new { index = rowIndex++, value = item };
var rpmArray = (from item in allDataQry where item.index % 4 == 0 select item.value).ToArray();
var multOffArray = (from item in allDataQry where item.index % 4 != 0 select item.value).ToArray();
 

[Plater]

As for why you get index of bounds:
Think about what happens on the last itteration for i, i would be the last index in your array. So what would curveData[i+1] (Note: i+1) be, out of bounds.