Trouble redefining an array with its values-CodePudding

Let's say we have an array as follows:

x = [4.0,0,0,2.0,0,0]

And we also have a bunch of positions (positions represent indexes 1 (basically indexes starting at 1):

unboundedVarsIndex = [3]

My objctive is basically to "merge" or "put togheter" the values of x such that in final we have the following:

x = [4.0 , 0, 0-2.0, 0, 0]

So basically,

for index in unboundedVarsIndex:
     x[index-1] = x[index-1] - x[index]

But this gives me the following output:

x = [4.0 , 0, -2.0, 2.0, 0, 0]

Which makes sense, since I did nothing to delete two from the array. I would like find a way to clear 2 from the array and also I would like to make this code work for more than 1 position, i.e., to make it work for example when we have this:

len(unboundedVarsIndex) >= 1

Take this as example: Let

unboundedVarsIndex = [1,2,3]

Then, for the same vector x defined in the beggining, I would like to get the following output:

x = [4.0 = x[0] - 0 = x[1], x[2] = 0 - 2.0 = x[3], x[4] = 0 - 0 = x[5]]

Thanks for any help in advance.

UPDATE Answering the comment: understand I can do that by doing unboundedVarsIndex.sort(reverse=True) but still this doesn't give me the output wanted. Let's say I do the following:

x = [4,0,0,2,0,0]
unboundedVarsIndex = [1,2,3]
unboundedVarsIndex.sort(reverse=True)
for index in unboundedVarsIndex:
    x.insert(index-1,x[index-1]-x[index])
    del x[index 1]
    del x[index]
print(x)

I get the output: x = [2,0,0] and this is not what I wanted. Where am I doing a mistake?

CodePudding user response：

I was able to solve my own issue using the following code:

x = [4,0,0,2,0,0]
unboundedVarsIndex = [1,2,3]
unboundedVarsIndex.sort(reverse=True)
for index in unboundedVarsIndex:
    if index-1 in unboundedVarsIndex:
        x[index] = x[index] - x[index 1]
        del x[index 1]
    else:
        x[index-1] = x[index-1] - x[index]
        del x[index]

Thanks for all the help in the comments from @jasonharper and @KarlKnetchel. Their help made me realise my mistakes and help me with the syntaxe.

CodePudding user response：

So you're trying to iterate through some given positions in the array, and for each position perform the following:

Update: array[position - 1] = array[position - 1] - array[position]
Remove: array.pop(position)

def redefine(arr, unbounded_var_positions):
    for position in unbounded_var_positions:
        if not arr:
            return
        redefine_index = position - 1
        if (redefine_index >= 0) and (redefine_index < len(arr) - 1):
            arr[redefine_index] = arr[redefine_index] - arr[redefine_index   1]
            arr.pop(redefine_index   1)

Which does the following:

>>> arr = [4, 0, 0, 2, 0, 0]
>>> unbounded_var_positions = [1, 2, 3]
>>> redefine(arr, unbounded_var_positions)
>>> arr
[4, -2, 0]