here's some code in the Wolfram Programming Language (the language
underlying Mathematica) illustring the use of pattern matching.
Society is a list of the attribute lists of people. As an illustration, we
will create a society consisting of eight people, each with two attributes.
In each person's attribute list,
the first element (which is a number) represents the person's name ,
the second element which is a list of numbers) is a list of the names of
the members of the person's social network.
society = {{1, {5, 7}},
{2, {}},
{3, {}},
{4, {1, 2}},
{5, {2, 7}},
{6, {2}}},
{7, {8}},
{8, {5}}}
We can modify society so that anyone who is in another person's social
network includes that person in their own social network (i.e., reciprocal
social connections).
symSoc = society /.
{a_Integer, b_} :> {a, Union[b, Cases[society, {x_, {___, a, ___}} :> x]]}
symSoc = {{1, {4, 5, 7}},
{2, {4, 5, 6}},
{3, {}},
{4, {1, 2}},
{5, {1, 2, 7, 8}},
{6, {2}},
{7, {1, 5, 8}},
{8, {5, 7}}}
how would this be done in J?
note: a pdf of the note set on the Wolfram Language in which the
expressions for society and symSoc appear on p. 42 can be downloaded at
http://library.wolfram.com/infocenter/MathSource/5216/
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