prosody
6092fc9b078b
util/iterators.lua

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util/iterators.lua @ 1659:6092fc9b078b

util.iterators: Add head() iterator, to return the first n items
author Matthew Wild <mwild1@gmail.com>
date Mon, 10 Aug 2009 15:07:32 +0100
parent 1522:569d58d21612
child 1660:ae2f60a20428
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1 -- Prosody IM
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2 -- Copyright (C) 2008-2009 Matthew Wild
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3 -- Copyright (C) 2008-2009 Waqas Hussain
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4 --
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5 -- This project is MIT/X11 licensed. Please see the
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6 -- COPYING file in the source package for more information.
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7 --
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8
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9 --[[ Iterators ]]--
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10
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11 -- Reverse an iterator
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12 function reverse(f, s, var)
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13 local results = {};
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14
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15 -- First call the normal iterator
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16 while true do
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17 local ret = { f(s, var) };
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18 var = ret[1];
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19 if var == nil then break; end
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20 table.insert(results, 1, ret);
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21 end
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22
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23 -- Then return our reverse one
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24 local i,max = 0, #results;
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25 return function (results)
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26 if i<max then
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27 i = i + 1;
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28 return unpack(results[i]);
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29 end
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30 end, results;
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31 end
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32
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33 -- Iterate only over keys in a table
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34 local function _keys_it(t, key)
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35 return (next(t, key));
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36 end
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37 function keys(t)
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38 return _keys_it, t;
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39 end
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40
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41 -- Iterate only over values in a table
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42 function values(t)
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43 local key, val;
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44 return function (t)
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45 key, val = next(t, key);
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46 return val;
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47 end, t;
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48 end
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49
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50 -- Given an iterator, iterate only over unique items
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51 function unique(f, s, var)
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52 local set = {};
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53
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54 return function ()
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55 while true do
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56 local ret = { f(s, var) };
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57 var = ret[1];
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58 if var == nil then break; end
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59 if not set[var] then
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60 set[var] = true;
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61 return var;
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62 end
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63 end
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64 end;
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65 end
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66
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67 --[[ Return the number of items an iterator returns ]]--
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68 function count(f, s, var)
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69 local x = 0;
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70
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71 while true do
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72 local ret = { f(s, var) };
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73 var = ret[1];
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74 if var == nil then break; end
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75 x = x + 1;
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76 end
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77
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78 return x;
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79 end
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80
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81 -- Return the first n items an iterator returns
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82 function head(n, f, s, var)
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83 local c = 0;
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84 return function (s, var)
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85 if c >= n then
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86 return nil;
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87 end
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88 c = c + 1;
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89 return f(s, var);
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90 end, s;
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91 end
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92
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93 -- Convert the values returned by an iterator to an array
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94 function it2array(f, s, var)
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95 local t, var = {};
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96 while true do
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97 var = f(s, var);
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98 if var == nil then break; end
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99 table.insert(t, var);
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100 end
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101 return t;
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102 end
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103
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104 -- Treat the return of an iterator as key,value pairs,
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105 -- and build a table
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106 function it2table(f, s, var)
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107 local t, var = {};
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108 while true do
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109 var, var2 = f(s, var);
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110 if var == nil then break; end
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111 t[var] = var2;
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112 end
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113 return t;
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114 end