"Compressing" a list of integers
<p>I have a list of integers as follows:</p>

<pre><code>my_list = [2,2,2,2,3,4,2,2,4,4,3]
</code></pre>

<p>What I want is to have this as a list os strings, indexed and 'compressed', that is, with each element indicated by its position in the list and with each successive duplicate element indicated as a range, like this:</p>

<pre><code>my_new_list = ['0-3,2', '4,3', '5,4', '6-7,2', '8-9,4', '10,3']
</code></pre>

<p>EDIT: The expected output should indicate that list elements 0 to 3 have the number 2, element 3, the number 3, element 5, the number 4, elements 6 and 7, the number 2, elements 8 and 9, number 4, and element 10, number 3. </p>

<p>EDIT 2: The output list need not (indeed cannot) be a list of integers, but a list of strings instead.</p>

<p>I could find many examples of finding (and deleting) duplicated elements from lists, but nothing along the lines of what I need.</p>

<p>Could someone point out a relevant example or suggest an algorithm for solving this?</p>

<p>Thanks in advance!</p>

<p>Like most problems involving cascading consecutive duplicates, you can still use <a href="https://docs.python.org/3/library/itertools.html#itertools.groupby" rel="nofollow">groupby()</a> for this. Just group indices by the value at each index.</p>

<pre><code>values = [2,2,2,2,3,4,2,2,4,4,3]
result = []

for key, group in itertools.groupby(range(len(values)), values.__getitem__):
    indices = list(group)

    if len(indices) &gt; 1:
        result.append('{}-{},{}'.format(indices[0], indices[-1], key))
    else:
        result.append('{},{}'.format(indices[0], key))

print(result)
</code></pre>

<p>Output:</p>

<pre><code>['0-3,2', '4,3', '5,4', '6-7,2', '8-9,4', '10,3']
</code></pre>

python list