[2] | 1 | ;+ |
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| 2 | ; |
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[230] | 3 | ; @file_comments |
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[493] | 4 | ; find the different elements of 2 matrices of positive whole numbers. |
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[2] | 5 | ; |
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[373] | 6 | ; see also <pro>union</pro> and <pro>inter</pro>. |
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| 7 | ; |
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[157] | 8 | ; @categories |
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| 9 | ; Calculation |
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[2] | 10 | ; |
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[232] | 11 | ; @param a {in}{required} |
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[230] | 12 | ; arrays of positive integers, which need |
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[372] | 13 | ; not be sorted. Duplicate elements are ignored, as they have no |
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| 14 | ; effect on the result |
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[2] | 15 | ; |
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[232] | 16 | ; @param b {in}{required} |
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[230] | 17 | ; see a |
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[2] | 18 | ; |
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[230] | 19 | ; @returns |
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[373] | 20 | ; an array containing the set of values in only a. |
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[2] | 21 | ; |
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[230] | 22 | ; The empty set is denoted by an array with the first element equal to |
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[2] | 23 | ; -1. |
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| 24 | ; |
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[232] | 25 | ; @restrictions |
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[230] | 26 | ; These functions will not be efficient on sparse sets with wide |
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[2] | 27 | ; ranges, as they trade memory for efficiency. The HISTOGRAM function |
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| 28 | ; is used, which creates arrays of size equal to the range of the |
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| 29 | ; resulting set. |
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| 30 | ; |
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[133] | 31 | ; @examples |
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[2] | 32 | ; |
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[371] | 33 | ; IDL> a = [2,4,6,8] |
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| 34 | ; IDL> b = [6,1,3,2] |
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[2] | 35 | ; |
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[495] | 36 | ; IDL> res=different(a,b) |
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[373] | 37 | ; 4 8 |
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| 38 | ; Right because 4 and 8 are in a but not in b ! |
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| 39 | ; |
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| 40 | ; IDL> res=different(b,a) |
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| 41 | ; IDL> print,res |
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| 42 | ; 1 3 |
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| 43 | ; |
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| 44 | ; Right because 1 and 3 are in b but not in a ! |
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| 45 | ; |
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[230] | 46 | ; @history |
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[232] | 47 | ; <a href="http://www.dfanning.com/tips/set_operations.html"/> |
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[2] | 48 | ; |
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[230] | 49 | ; @version |
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| 50 | ; $Id$ |
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[133] | 51 | ; |
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[2] | 52 | ;- |
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[230] | 53 | FUNCTION different, a, b |
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[114] | 54 | ; |
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| 55 | compile_opt idl2, strictarrsubs |
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| 56 | ; |
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[2] | 57 | |
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| 58 | ; = a and (not b) = elements in A but not in B |
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| 59 | |
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| 60 | mina = Min(a, Max=maxa) |
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| 61 | minb = Min(b, Max=maxb) |
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| 62 | IF (minb GT maxa) OR (maxb LT mina) THEN RETURN, a ;No intersection... |
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| 63 | r = Where(Histogram(a, Min=mina, Max=maxa) $ |
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| 64 | *(1-Histogram(b, Min=mina, Max=maxa)), count) |
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| 65 | IF count eq 0 THEN RETURN, -1 ELSE RETURN, r + mina |
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| 66 | END |
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