MathGroup Archive 1998

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Request for help: working with multi-level lists


I have a list of 10 elements, each of which is a list of three elements
(let's say in each case an integer, a real number, and a string). I am
looking for the most elegant way to select those first-level elements
(i.e., the lists) whose integer element is equal to a particular value
(let's say "1"), and then to obtain the mean of the real number
elements of the lists selected.  This seems as if it should be simple,
but everything I try leads to Part specification errors.  Any help
would be greatly appreciated.


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