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    <p>This does the job, if I undesrtood correctly:</p> <pre><code>l = [[10312, -13.069404602050781], [10313, -28.044403076171875], [10314, -32.765602111816406], [10315, -47.353294372558594], [10312, -63.069404602050781], [10313, -78.044403076171875], [10314, -82.765602111816406], [10315, -97.353294372558594]] from pprint import pprint d = {} for i,(x,n) in enumerate(l): print i,x,n if x in d: l[d[x]].append(n) del l[i][:] else: d[x] = i l = filter(None,l) pprint (l) </code></pre> <p>.</p> <h3>Edit</h3> <p>Here's a better algorithm because there's no more the filtering of the list done by the instruction <code>l = filter(None,l)</code> , so the transformation is in-place.</p> <p>This instruction <code>l = filter(None,l)</code> creates a new list, that is to say a new object at another address in the memory: then the above code don't realize an in-place transformation of the list.<br> The following one performs such an in-place transformation, as it is put in evidence by the printing of the identities (id est addresses) of the list <code>l</code> before and after its treatment.</p> <pre><code>l = [[10312, -13.069404602050781], [10313, -28.044403076171875], [10314, -32.765602111816406], [10312, -63.069404602050781, -55.4444], [20666, -91, -92, -93, -94], [10315, -47.353294372558594], [10314, -82.765602111816406], [10315, -97.353294372558594], [10313, -78.044403076171875], [20666, -40.33, -94, -50.33, -91, -93] ] from pprint import pprint d = {} to_del = [] print 'id(l) before : ',id(l) pprint (l) for i,subli in enumerate(l): if subli[0] in d: d[subli.pop(0)].extend(subli) to_del.insert(0,i) else: d[subli[0]] = subli for i in to_del: del l[i] print '\nid(l) after : ',id(l) pprint (l) </code></pre> <ul> <li><p>Note that in the former code, the values of <code>d</code> were the indexes of the sublists of <code>l</code>.<br> Now <strong>in this new code, the values of <code>d</code> are directly the sublists of <code>l</code></strong>.<br> It is more pythonic to reference objects directly, instead of referecing them indirectly through their indexes in the list whose they are elements of.</p></li> <li><p>The list <code>to_del</code> records the indexes of the sublists that will be deleted after the first loop. Each index added is inserted at the beginning of <code>to_del</code> (not appended to it) so that the second loop ( <code>for i in to_del</code> )will <strong>run retrogressively</strong> through the list <code>l</code> , which <strong>is the condition that must be respected when elements of a list are deleted on the basis of their indexes</strong>.</p></li> </ul> <p>The instruction <code>d[subli.pop(0)].extend(subli)</code> may seem somewhat a little difficult to understand. </p> <p>The operations begins with the execution of <code>subli.pop(0)</code> : this instruction triggers the extraction of the element indexed 0 from the sublist <code>subli</code> and returns it.<br> Then <code>d[subli.pop(0)]</code> furnishes the object <strong>subli.pop(0)</strong> to <code>d</code> as a key, meanwhile this objects is removed from the sublist <code>subli</code>.<br> So, at this point, the sublist <code>subli</code> has been shortened of its first element, as if the instruction <code>subli[:] = subli[1:]</code> had been performed <sup>see remark at the bottom</sup>. </p> <p>Next, the sublist <code>d[subli.pop(0)]</code> , that had been precedently encountered in <code>l</code> during the iteration through list <code>l</code> , is extended with the elements remaining in the sublist <code>subli</code> after this one has been shortened, that is to say with the elements that were indexed <code>1</code> to <code>len(subli)-1</code> BEFORE it was shortened. But, as <code>subli</code> has been shortened, we only write <code>subli</code>, not <code>subli[1:]</code>. </p> <p>And it works ! Result:</p> <pre><code>id(l) before : 18732936 [[10312, -13.069404602050781], [10313, -28.044403076171875], [10314, -32.765602111816406], [10312, -63.06940460205078, -55.4444], [20666, -91, -92, -93, -94], [10315, -47.353294372558594], [10314, -82.7656021118164], [10315, -97.3532943725586], [10313, -78.04440307617188], [20666, -40.33, -94, -50.33, -91, -93]] id(l) after : 18732936 [[10312, -13.069404602050781, -63.06940460205078, -55.4444], [10313, -28.044403076171875, -78.04440307617188], [10314, -32.765602111816406, -82.7656021118164], [20666, -91, -92, -93, -94, -40.33, -94, -50.33, -91, -93], [10315, -47.353294372558594, -97.3532943725586]] </code></pre> <p>.</p> <p>If you want that only non-redudant elements be added to a previously existing sublist, it must be:</p> <pre><code>for i,subli in enumerate(l): print 1,subli if subli[0] in d: precsubli = d[subli.pop(0)] precsubli.extend(el for el in subli if el not in precsubli) to_del.insert(0,i) else: d[subli[0]] = subli </code></pre> <p>.</p> <h3>Important remark</h3> <p>Note the difference :</p> <pre><code>N = [10000,2,3,4] initial_id = id(N) print initial_id, N N = N[1:] print id(N), N print '%d==%d : %s' %\ (initial_id, id(N), initial_id==id(N) ) print '------------------' A = ['HEY','b','c','d'] initial_id = id(A) print initial_id, A A[:] = A[1:] print id(A), A print '%d==%d : %s' %\ (initial_id, id(A), initial_id==id(A) ) </code></pre> <p>result</p> <pre><code>18669480 [10000, 2, 3, 4] 11868480 [2, 3, 4] 18669480==11868480 : False ------------------ 18731816 ['HEY', 'b', 'c', 'd'] 18731816 ['b', 'c', 'd'] 18731816==18731816 : True </code></pre> <p>That means that <code>A</code> is modified in-place, while object referenced by <code>N</code> is not: the instruction <code>N[1:]</code> builds a new object, at a location in the memory elsewhere than the location of the object referenced by <code>N</code>.</p>
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    1. USeyquem
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    1. COthanks, i will try it
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    2. COyour first script eyquem works perfectly, considering that number of elem (1st colum) is of known length and all the other cols will carry the same len as col 1
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      1. USfabio.geraci
 

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