Array Processing in Livecode

Question

I'm pretty happy with the idea that Livecode Arrays are actually associative arrays, but I'm wondering if you can access them by index, rather than key?

I want to put 5 strings in to an array, so all I know how to do so far is

put "fred" into myArray[1]
put "wilma" into myArray[2]
put "barney" into myArray[3]
put "betty" into myArray[4]
put "dino" into myArray[5]

This creates me my array, and I can iterate it thru it by declaring a variable and incrementing it in a loop, accessing it with myArray[index]

In this case though, it feels to me like this is still doing a keyed lookup, and not using the index to refer to a position within the array.

Where this really hurts me is when I do

delete variable myArray[3]

Sure enough, barney gets deleted, and my array now thinks there are 4 items in it. So, if I asked for the third member of the array again, coming as I do from a Java / C background, I'd expect to get "betty" - but I don't - I get nothing, as the is now no member of the array keyed by "3"

So, can I access the array by index, or do I always have to go for a keyed retrieval?

score 2 · Answer 1 · answered Oct 31 '14 at 14:58

I know this is an old thread, but coming from other languages, I've also been struggling with the lack of a true linear array in LiveCode. So for anyone else who happens upon this thread:

Since LiveCode seems to have a pretty full compliment of text methods (chunk expressions), I've been using comma delimited strings in variables instead of arrays.

In the original example above, deleting item 3, "barney" from a string, would move "betty" to the item 3 position. It would also return a length of 4 instead of 5.

This is definitely a different way of thinking, but in the absence of a linear array this has been working for me.

score 1 · Accepted Answer · answered Nov 18 '13 at 20:39

1

You can do this, but you still need to use the index. Since you want to use a numeric index, you need to sort the keys. (LiveCode arrays are fast, because the keys are unsorted).

put the keys of myArray into myKeys
sort the lines of myKeys numeric
put myArray[line 3 of myKeys] into myName

You can make this a (fake) one-liner by using a function:

-- usage:
put myArray[sortedKey(3,myArray)] into myName

function sortedKey(theIndex,theArray)
  put theKeys of theArray into myKeys
  sort the lines of myKeys numeric
  return line theIndex of myKeys
end sortedKey

Evidently, there are multiple solutions to this problem. Keep in mind that sorting slows down the handling of the array.

answered Nov 18 '13 at 20:39

Mark

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Thanks Mark - but I'm not sure how that helps me - In my example above, wouldn't I still be left with Keys of 1,2,4 & 5, rather than 1,2,3, & 4 after I delete the item with a key of 3 and re-sort the array? – DaveH Nov 18 '13 at 21:16
Dave, the function I wrote does exactly what you want. However, you can't access the keys by number directly, because they are unsorted. So, the real answer is, you can't do exactly what you want, but there is a way around it. Please, give the script a try. – Mark Nov 18 '13 at 21:28
Note that `put myArray[line 2 of the keys of myArray]` may return myArray[10]. – Mark Nov 18 '13 at 21:53
haven't had chance to try this out yet but am I right in thinking that "line 3 of myKeys" is getting the third element out of the mkKeys variable ( whatever type that is )? If that's the case then I think I've got it :) - If it _is_ the case then could I also do "put line 3 of myArray into myName" ? – DaveH Nov 19 '13 at 13:17
You can't get line 3 of myArrray and since you want to use numeric keys in sorted order you have to sort them before getting the third line of the keys. So, yes line 3 of myKeys gets the third line out of the myKeys variable but that's not the same as getting the third line from the array. (Also, I wouldn't call a line from a list of keys an element because elements in an array are what the keys refer to). – Mark Nov 19 '13 at 13:43

score 1 · Answer 3 · answered Nov 18 '13 at 23:10

You need to implement the functionality on top of arrays. Here's a couple of commands that might help you:

Remove the first instance of a known element from an array

command ArrayRemove @pArray,pValue
   local tRemoved = "false"
   repeat with tIndex = min(replaceText(keys(pArray),cr,comma)) to max(replaceText(keys(pArray),cr,comma))
      if tRemoved then
         put pArray[tIndex] into pArray[tIndex-1]
      else if pArray[tIndex] = pValue then
         delete variable pArray[tIndex]
         put true into tRemoved
      end if
   end repeat
   if tRemoved then
      delete variable pArray[tIndex]
   end if
end ArrayRemove

Remove a known index from an array

command ArrayRemoveIndex @pArray,pIndex
   repeat with tIndex = pIndex+1 to max(replaceText(keys(pArray),cr,comma))
      put pArray[tIndex] into pArray[tIndex-1]
   end repeat
   delete variable pArray[tIndex]
end ArrayRemoveIndex

Note that these commands also work with other stuff like Queues so the indexes might not start with 1. You could remove the max etc and replace with the number of elements of pArray if you know your arrays are 1..n

If you're not positive that pIndex is within the range of the indexes of your array then you would need to add some checks to ArrayRemoveIndex

score 1 · Answer 4 · answered Nov 19 '13 at 11:25

1

Dave. You always have to refer to an array element by the key name. You can write a small function to do what you want;

function arrayIndex @pArray, pIndex
   return pArray[line pIndex of the keys of pArray]
end arrayIndex

After you delete element "3", You can then access element number 3 (which is key "4") with;

put arrayIndex(myArray, 3) into tValue

HTH :D

answered Nov 19 '13 at 11:25

splash21

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This won't work because you're not sorting the arrays. You can use @ but you don't have to. I think that a function without @ is easier to understand. – Mark Nov 19 '13 at 13:45

Array Processing in Livecode

4 Answers4