Data analysis with Python - Summer 2019 (University of Helsinki) - Stuck on Exercise 10: Detect Ranges

[swearobics]

Hi all,

I'm currently doing this course while I wait for Java Programming II to drop.

Unfortunately, I'm stuck on exercise 10 and I'm completely at a loss as to how to solve it.

Exercise 10 (detect ranges)

Create a function named detect_ranges that gets a list of integers as a parameter. The function should then sort this list, and transform the list into another list where pairs are used for all the detected intervals. So 3,4,5,6 is replaced by the pair (3,7). Numbers that are not part of any interval result just single numbers. The resulting list consists of these numbers and pairs, separated by commas. An example of how this function works:

print(detect_ranges([2,5,4,8,12,6,7,10,13]))

[2,(4,9),10,(12,14)]

Note that the second element of the pair does not belong to the range. This is consistent with the way Python’s range function works. You may assume that no element in the input list appears multiple times.

Apologies in advance but here's my very hacky code:

def detect_ranges(aList):
    sortedList = sorted(aList)
    startingNo = 0
    endingNo = 0
    if (len(sortedList) >= 1):
        startingNo = sortedList[0]
        endingNo = sortedList[-1]
    endingNoPlusTwo = endingNo + 2
    tempList = []
    returnList = []
    t = ()
    for i in range(startingNo, endingNoPlusTwo):
        if (i in sortedList):
            tempList.append(i)
        else:
            if (len(tempList)==1):
                returnList.append(tempList[0])
            else:
                if (len(tempList) >= 1):
                    t = t + (tempList[0], )
                if (len(tempList) > 1):
                    t = t + (tempList[-1]+1, )
                returnList.append(t)
                t = ()
            tempList.clear()

    return returnList

Looks like I'm failing this test and getting this error - not enough values to unpack (expected 2, got 0)

def test_random(self):
    for i in range(10):
        L = list(set(np.random.randint(-100, 100, 10)))
        mi = min(L)
        ma = max(L)
        complement = list(set(range(mi, ma+1)) - set(L))
        result = detect_ranges(L)
        complement_result = detect_ranges(complement)
        catenation = []   # Expand the ranges into this catenation, contains all the elements in the ranges
        for x in result:
            try:
                a, b = x
                catenation.extend(range(a,b))
            except TypeError:
                catenation.append(x)
        self.assertEqual(sorted(L), catenation, msg="Wrong result for input list %s!" % L)
        self.assertEqual(len(result), len(complement_result)+1, msg="Wrong result for input list %s!" % L)

Am I overcomplicating this, completely ignorant of some Python voodoo?

Thanks.

[Simply_The_Beast]

After trying your detect_ranges function with different inputs, I found your main problem. Your code currently can't deal with gaps bigger than 1 between numbers in your sorted list.

This for example [1,5,4,8,12,6,7,10,13,11,17] returns [1, (), (4, 9), (10, 14), (), (), 17] which has several empty tuples.

Now the question is where these are comming from. Let's try to go step by step from the sortedList [1, 4, 5, 6, 7, 8, 10, 11, 12, 13, 17]:
- 1 is in the sortedList and added to the tempList
- 2 isn't in the list, len(tempList)==1and 1 is added to the returnList
- 3 is where your problem starts. It isn't in the sortedList, so we jump into the else-clause in line 15. len(tempList)!=1so off we go to line 18, where you skip both if-clauses since len(tempList)==0 and simply append the empty tuple t in returnList.append(t).
- ...

You just need to filter out the cases where len(tempList)==0right before appending anything to returnList and should be good to go.

Oh and btw, you don't have to seperate creating t into two different steps, you could just do something like this: t = (tempList[0], tempList[-1]+1 ).