Well, the format of that last post was a bit messy. Here's a second try:
The
animal control officer wants to keep track of the animals in a city.
The officer tags all the animals with a serial number.
He keeps a list of all the animals he has tagged, along with each serial
number.
list
┌────┬───┬───┬───┬───┬───┬───┬────┬───┬───┬───┬───┬───┬────┬───┐
│bird│cow│cow│dog│cow│cow│cow│bird│dog│cat│dog│pig│dog│bird│pig│
├────┼───┼───┼───┼───┼───┼───┼────┼───┼───┼───┼───┼───┼────┼───┤
│1 │2 │3 │4 │5 │6 │7 │8 │9 │10 │11 │12 │13 │14 │15 │
└────┴───┴───┴───┴───┴───┴───┴────┴───┴───┴───┴───┴───┴────┴───┘
The officer now wants to make a second list showing each type
of animal along with all the serial numbers tagged for each animal.
list2
┌────┬──┬──┬──┬──┬─┐
│bird│1 │8 │14│ │ │
├────┼──┼──┼──┼──┼─┤
│cow │2 │3 │5 │6 │7│
├────┼──┼──┼──┼──┼─┤
│dog │4 │9 │11│13│ │
├────┼──┼──┼──┼──┼─┤
│cat │10│ │ │ │ │
├────┼──┼──┼──┼──┼─┤
│pig │12│15│ │ │ │
└────┴──┴──┴──┴──┴─┘
What is the shortest J expression to generate list2?
(Tacit would be nice)
Skip Cave
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