Sunday, February 12, 2012


Ordering reads out the order of the elements of a List if they were sorted. So in the Table below, the first row is the list itself, the second row shows the list sorted, and the third row shows the Ordering of the list: the eighth element (1) would be first, the third element (2) would be second, the fifth element (3) would be third, the 4th element would be last, etc. Incidentally I use SeedRandom here so that if you evaluate the code you will get the same random sample as I got.

In[208]:= SeedRandom@135; aList = RandomSample[Range@10, 10]

Out[208]= {7, 5, 2, 10, 3, 6, 4, 1, 9, 8}

In[209]:= {aList, Sort@aList, Ordering@aList} //
 TableForm[#, TableHeadings -> {{"aList", "Sort", "Ordering"}, {}}] &

What are the Positions of the largest two elements in aList? Use this syntax:

In[210]:= Ordering[aList, {-2, -1}]

Out[210]= {9, 4}

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