Forum Discussion

btpoole's avatar
btpoole
Channel Surfer
11 years ago

Array Range

Is there any way to extract a set number of values stored in an array. For example in the the array myarray I only want the first 10 entries in the array.
Thanks

6 Replies

  • I don't think there's anything simpler than the obvious

    first_ten = []
    for i = 0 to 9
    first_ten.Push(my_array[i])
    end for


    --Mark
  • btpoole, did you mean if there is an elegant way to do that, like array slicing in Python:
    >>> a = [00,11,22,33,44]
    >>> a[2:4]
    [22, 33]
    >>> a[3:]
    [33, 44]
    >>> a[:-2]
    [0, 11, 22]
    >>> a[::-2]
    [44, 22, 0]

    The answer would be "no". Good idea for future enhancement though, to add ifArray.slice(...)
  • I just thought, writing a universal slice function won't be hard - and here is what i sketched:

    function arraySlice(arr, start=invalid, finish=invalid, step_=1):
    if step_ = 0 then print "ValueError: slice step cannot be zero" : STOP
    if start = invalid then if step_ > 0 then start = 0 else start = arr.count() - 1
    if finish = invalid then if step_ > 0 then finish = arr.count() - 1 else finish = 0
    if start < 0 then start = arr.count() + start 'negative counts backwards from the end
    if finish < 0 then finish = arr.count() + finish
    res = [ ]
    for i = start to finish step step_:
    res.push(arr[i])
    end for
    return res
    end function

    And here is testing it to act like the python examples above:

    BrightScript Debugger> a = [00,11,22,33,44]
    BrightScript Debugger> ? arraySlice(a, 2, 3)
    22
    33

    BrightScript Debugger> ? arraySlice(a, 3)
    33
    44

    BrightScript Debugger> ? arraySlice(a, invalid, -3)
    0
    11
    22

    BrightScript Debugger> ? arraySlice(a, invalid, invalid, -2)
    44
    22
    0


    Just like in Python it can slice forward - or backwards (-1 step reverses the slice) - or from the beginning to certain point - or from a position till the end - or every N-th element (when step is N>1). One difference is that it's inclusive of the slice end, it's easier for beginners that way (and was easier for me to write too).
  • btpoole's avatar
    btpoole
    Channel Surfer
    Thanks for the input. I was hoping I was missing a part in sdk that provided a dot operator where a range could be extracted. I can live with the small code to do it, but was looking for a one liner.
    Thanks again
  • "btpoole" wrote:
    I can live with the small code to do it, but was looking for a one liner.

    I just wrote you a little gem* of a function that does in one line what you asked for:
    mySlice = arraySlice(myArray, 0, 9)  'returns the 10 first elements 
    Is that not good enough? It even does party tricks, like say when called with no extra params, `arraySlice(arr)` makes a copy of the array.

    Or would you like this functionality added to roArray, presumably in optimized implementation? You and me both, brother... where do i sign? 😉

    (*) all credit goes to
    a) Python's slice notation/concept
    b) optional parameters capability in BrightScript
    c) the way FOR loop loops
  • btpoole's avatar
    btpoole
    Channel Surfer
    EnTerr, thanks a million. I had created the script using the for/end for but will use this in its place.
    Thanks again