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list splitting


osbornece at cardiff.ac.uk (c. osborne)
[mg4872] list splitting
writes

>i have  some mathematica code which generates a list of results in  
>theform ;
>{{{ 1, 2, {a-> 3, b-> 4, c-> 4}, 5}, {6, 7, {a-> 8, b-> 9, ...}}}
>what i would like to do is to be able to select those parts of the
>list which have a>0, b> 4 etc.

Cases should help, but you may have to use the levelspec setting.

?Cases
Cases[{e1, e2, ...}, pattern] gives a list of the ei that match the
pattern.
Cases[{e1, ...}, pattern -> rhs] or Cases[{e1, ...}, pattern :>  
rhs] gives a list of the values of rhs corresponding to the ei that  
match the pattern.
Cases[expr, pattern, levelspec] gives a list of all parts of expr  
on levels specified by levelspec which match the pattern.

Allan Hayes
hay at haystack.demon.co.uk





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