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util/iterators.lua

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util/iterators.lua @ 919:75b8afb79143

util.iterators: New iterators library
author Matthew Wild <mwild1@gmail.com>
date Wed, 25 Mar 2009 03:01:10 +0000
child 1522:569d58d21612
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1 --[[ Iterators ]]--
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2
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3 -- Reverse an iterator
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4 function reverse(f, s, var)
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5 local results = {};
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6
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7 -- First call the normal iterator
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8 while true do
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9 local ret = { f(s, var) };
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10 var = ret[1];
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11 if var == nil then break; end
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12 table.insert(results, 1, ret);
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13 end
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14
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15 -- Then return our reverse one
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16 local i,max = 0, #results;
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17 return function (results)
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18 if i<max then
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19 i = i + 1;
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20 return unpack(results[i]);
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21 end
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22 end, results;
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23 end
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24
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25 -- Iterate only over keys in a table
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26 local function _keys_it(t, key)
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27 return (next(t, key));
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28 end
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29 function keys(t)
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30 return _keys_it, t;
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31 end
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32
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33 -- Iterate only over values in a table
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34 function values(t)
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35 local key, val;
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36 return function (t)
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37 key, val = next(t, key);
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38 return val;
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39 end, t;
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40 end
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41
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42 -- Given an iterator, iterate only over unique items
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43 function unique(f, s, var)
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44 local set = {};
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45
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46 return function ()
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47 while true do
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48 local ret = { f(s, var) };
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49 var = ret[1];
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50 if var == nil then break; end
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51 if not set[var] then
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52 set[var] = true;
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53 return var;
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54 end
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55 end
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56 end;
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57 end
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58
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59 --[[ Return the number of items an iterator returns ]]--
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60 function count(f, s, var)
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61 local x = 0;
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62
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63 while true do
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64 local ret = { f(s, var) };
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65 var = ret[1];
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66 if var == nil then break; end
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67 x = x + 1;
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68 end
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69
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70 return x;
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71 end
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72
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73 -- Convert the values returned by an iterator to an array
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74 function it2array(f, s, var)
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75 local t, var = {};
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76 while true do
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77 var = f(s, var);
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78 if var == nil then break; end
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79 table.insert(t, var);
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80 end
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81 return t;
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82 end
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83
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84 -- Treat the return of an iterator as key,value pairs,
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85 -- and build a table
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86 function it2table(f, s, var)
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87 local t, var = {};
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88 while true do
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89 var, var2 = f(s, var);
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90 if var == nil then break; end
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91 t[var] = var2;
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92 end
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93 return t;
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94 end