Question

运行我的代码时，我一直收到以下错误。

我的代码：

class Integer
  def num_digits
    Math.log10(self).to_i + 1
  end

  def p(t)
    case t
    when 3
      return self * (self + 1) / 2
    when 4
      return self**2
    when 5
      return self * ((3 * self) - 1) / 2
    when 6
      return self * ((2 * self) - 1)
    when 7
      return self * ((5 * self) - 3) / 2
    when 8
      return self * ((3 * self) - 2)
    end
  end
end

$p3 = [], $p4 = [], $p5 = [], $p6 = [], $p7 = [], $p8 = []
$polygonals = [$p3, $p4, $p5, $p6, $p7, $p8]

(3..8).each_with_index do |t, index|
  i = 1
  until i == 150
    $polygonals[index] << i.p(t)
    i += 1
  end
end

$polygonals.each { |array| array.reject! { |x| x.num_digits != 4 } }

错误：

`block (2 levels) in <main>': undefined method `num_digits' for []:Array (NoMethodError)

但是，如果我将最后一行代码更改为：

$polygonals.each { |array| array.each { |x| x.reject! { |y| y.num_digits != 4 } } }

我收到错误：

`block (2 levels) in <main>': undefined method `reject!' for 1:Fixnum (NoMethodError)

x如何在第一种情况下输入array，在第二种情况下输入Fixnum？

Answer 1

修改失败的原因如下所示：

irb(main):072:0> $polygonals = [$p3, $p4, $p5, $p6, $p7, $p8] => [[[], [], [], [], [], []], [], [], [], [], []]

观察你的第一个元素是怎样的。不完全像你预期的那样，对吗？

实际上你有两个。看看$ polygonals [0]的样子：


IRB（主）：066：0＆GT; $ polygonals [0] =＆GT; [[]，[1,4,9,16,25,36,49,64，   81,100,121,144,169,196,225,256,289,324,361,400,441,484，   529,576,625,676,729,784,841,900,961,1024,1089,1156,1225，   1296,1369,1444,1521,1600,1681,1764,1849,1936,2025,2116,2209，   2304,2401,2500,2601,2704,2809,2916,3025,3136,3249,3364，   3481,3600,3721,3844,3699,4096,4225,4356,4489,4624,4761，   4900,5041,5184,5329,5476,5625,5776,5929,6084,6241,6400，   6561,6724,6889,7056,7225,7396,7569,7744,7921,8100,8281,8464，   8649,8836,9025,9216,9409,9604,9801,10000,10201,10404,10609，   10816,11025,11236,11449,11664,11881,11200,12321,12544,12769，   12996,13225,13458,13689,13924,14161,14400,14641,14884,15129，   15376,15625,15876,16129,16384,16641,16900,17161,17424,17689，   17956,18225,18491,18776,19044,19321,19600,1881,1 20164,20449，   20736,21025,21316,21609,21904,22201]，[1,5,12,22,35,51,70，   92,117,145,176,210,247,287,330,376,425,477,532,590,651，   715,782,852,925,1001,180,1162,1247,1335,1426,1520,1617，   1717,1820,1926,2035,2147,2262,2380,2501,2625,2752,2882，   3015,3151,3290,3432,3577,3725,3876,4030,4187,4347,4510,4676，   4845,5017,5192,5370,5551,5735,5922,6112,6305,6501,6700，   6902,7107,7315,7526,7740,7957,8177,8400,8626,8855,9087，   9322,9560,9801,10045,10292,10542,10795,11051,11310,11572，   11837,12105,12376,12650,12927,13207,13490,13776,14065,14357，   14652,14950,15251,15555,15862,16172,16485,16801,17120,17442，   17767,18095,1842,18760,19097,19437,19780,20126,20475,20827，   21182,21540,21901,22265,22632,23002,23375,23751,24130,24512，   24897,25285,25676,26070,26467,26867,27270,27676,28085,28497，   28912,29330,29751,30175,30602,31032,31465,31901,32340,32782，   33227]，[1,6,15,28,45,66,91,120,153,190,231,276,325,378，   435,496,561,630,703,780,861,946,1035,1128,1225,1326,1431，   1540,1653,1770,1891,2016,2145,2278,2415,2556,2701,2850，   3003,3160,3321,3486,3655,3828,4005,4186,4371,4560,4753，   4950,5151,5356,5565,5778,5995,6216,6441,6670,6903,7140，   7381,7626,7875,8128,8385,8646,8911,9180,9453,9730,10011，   10296,10585,10878,11175,11476,11781,12090,12403,12720,13041，   13366,13695,14028,14365,14706,15051,15400,15753,16110,16471，   16836,17205,17578,17955,18336,18721,19110,19503,19900,20301，   20706,21151,21528,21945,22366,22791,23220,23655,24090,24531，   24976,25425,25878,26335,26796,27261,27730,28203,28680,29161，   29646,30135,30628,31125,3162,32131,32640,33153,33670,34191，   34716,35245,35778,36315,36856,37401,37950,38503,39060,39621，   40186,40755,41328,41905,42486,43071,43660,44253]，[1,7,18，   34,55,81,112,148,189,235,286,342,403,469,540,616,697，   783,874,970,1071,1177,1288,1404,1525,1651,1782,1918,2059，   2205,2356,2512,2673,2839,3010,3186,3367,3553,7 3744,3940，   4141,4377,4558,4774,4995,5221,5452,5688,5929,6175,6426，   6682,6943,7209,7480,7756,8037,8323,8614,8910,9211,9517，   9828,10144,10465,10791,11122,11458,11799,12145,12496,12852，   13213,13579,13950,14326,14707,15093,15484,15880,16281,16687，   17098,17514,17935,18361,187922,19228,19669,20115,20566,21022，   21483,21949,22420,22896,23377,23863,24354,24850,25351,25857，   26368,26884,27405,27931,28462,28998,29539,30085,30636,31192，   31753,32319,32890,33466,34047,34633,35224,35820,36421,37027，   37638,38254,38875,39501,40132,40768,41409,42055,42706,43362，   44023,44689,45360,46036,46717,47403,48094,48790,49491,50197，   50908,51624,52345,53071,53802,54538,55279]，[1,8,21,40,65，   96,133,176,225,280,341,408,481,560,645,736,833,936,1045，   1160,1281,1408,1541,1680,1825,1976,2133,2296,2465,2640，   2821,3008,3201,3400,3605,3816,4033,4256,4485,4720,4961，   5208,5461,5720,5985,6256,6533,6816,7105,7400,7701,8008,8321，   8640,8965,9296,9633,9976,10325,10680,11041,11408,11781，   12160,12545,12936,13333,13736,14145,14560,14981,15408,15841，   16280,16725,17176,17633,18096,18565,19040,19521,20008,20501，   21000,21505,22016,22533,23056,23585,24120,24661,25208,25761，   26320,26885,27456,28033,28616,29205,29800,30401,31008,31621，   32240,38665,33491,34133,34776,35425,36080,36741,37408,38081，   38760,39445,40136,40833,41536,42245,42960,43681,44408,45141，   45880,46625,47376,48133,488896,49665,50440,51221,52008,52801，   53600,54405,55216,56033,56856,57685,58520,59361,60208,61061，   61920,62785,63656,64533,65416,66305]，1,3,6,10,15,21,28，   36,45,55,66,78,91,105,120,136,153,171,190,210,231,253，   276,300,325,351,378,406,435,465,496,528,561,595,630,666，   703,741,780,820,861,903,946,990,1035,1081,1128,1176,1225，   1275,1326,1378,1431,1485,1540,1596,1653,1711,1770,1830，   1891,1953,2016,2080,2145,2211,2278,2346,2415,2485,2556，   2628,2701,2775,2850,2926,3003,3081,3160,3240,3321,3403,3486，   3570,3655,3741,3828,3916,4005,4095,4186,4278,4371,4465，   4560,4656,4753,4851,4950,5050,5151,5253,5356,5460,5565，   5671,5778,5886,5995,6105,6216,6328,6441,6555,6670,6786，   6903,7021,7140,7260,7381,7503,7626,7750,7875,8001,1812,8256，   8385,8515,8646,8778,8911,9045,9180,9316,9453,9591,9730，   9870,10011,10153,10296,10440,10585,10731,10878,11026,11175]

这就是你的$ polygonals [1]的样子：


IRB（主）：067：0＆GT; $ polygonals [1] =＆GT; [1,4,9,16,25,36,49,64,81，   100,121,144,169,196,225,256,289,324,361,400,441,484,529，   576,625,676,729,784,841,900,961,1024,1089,1156,1225,1296，   1369,1444,1521,1600,1681,1764,1849,1936,2025,2116,2209，   2304,2401,2500,2601,2704,2809,2916,3025,3136,3249,3364，   3481,3600,3721,3844,3699,4096,4225,4356,4489,4624,4761，   4900,5041,5184,5329,5476,5625,5776,5929,6084,6241,6400，   6561,6724,6889,7056,7225,7396,7569,7744,7921,8100,8281，   8464,8649,8836,9025,9216,9409,9604,9801,10000,10201,10404，   10609,10816,11025,11236,11449,11664,11881,11200,12321,12544，   12769,12996,13225,13458,13689,13924,14161,14400,14641,14884，   15129,15376,15625,15876,16129,16384,16641,16900,17161,17424，   17689,17956,18225,18491,1876,19044,19321,19600,19881,20164，   20449,20736,21025,21316,21609,21904,22201]

Answer 2

这一行上的逗号

 $p3 = [], $p4 = [], $p5 = [], $p6 = [], $p7 = [], $p8 = []

不要做你的想法。在红宝石

 a = 1,2

将a设置为[1,2]，因此将$p3设置为

 [[], [], [], [], [], []]

如果您将这些分配放在单独的行上或使用;而不是逗号，那么这些变量将初始化为您所期望的。

Answer 3

首先，它通常被认为是扩展class Integer def num_digits Math.log10(self).to_i + 1 end end等核心类的不良做法。您应该只在特殊情况下执行此操作，在这种情况下，您提供应用程序可以在整个过程中使用的通用，有用的行为。

您编写的两种方法都是何时执行此操作的不良示例：

123.num_digits == 3

当你可以做一些像123.to_s.length == 3这样的事情时，为什么还要使用这种数学技巧（def p(t) case t when 3 return self * (self + 1) / 2 # ... when 8 return self * ((3 * self) - 2) end end end）？

这到底是什么？！ 3..8的含义是什么，为什么该方法仅适用于整数nil（否则返回Integer）？我猜它是计算多边形数字，在这种情况下你应该这样命名。这在def rename_me(x, y) # What are x and y? What IS this method? Use real words! case y when 3 x * (x + 1) / 2 # ... when 8 x * ((3 * x) - 2) end end类中没有位置;只是让它成为一个单独的方法，并更好地命名：

接下来，永远不要使用全局变量，除非你有充分的理由。在ruby中，以$polygonals开头的变量名称是全局的。而不是polygonals，只需定义x = 1, y = 2等变量。

接下来，学习如何在ruby中定义变量。编写像x == [1, 2]这样的代码并没有按照你的想法行事;这实际上是设置y == 2和x, y = 1, 2。这里的意图是定义变量的可能简写是：x == 1设置y == 2和def rename_me(x, y) # What are x and y? What IS this method? Use real words! case y when 3 x * (x + 1) / 2 # ... when 8 x * ((3 * x) - 2) end end polygonals = ([(1..149)] * 6) .map.with_index do |range, index| range .map { |x| rename_me(x, index + 3) } .select { |x| x.to_s.length == 4 } end - 但我不会像这样推荐1行定义;把它放在2行上。

考虑到所有这一切，以下是我将以更多＆＃34; ruby方式编写完整代码的方式＆＃34;：

然而（!!）你应该使用比我上面更好的变量名。不要只调用i等东西，除非它们只是划痕变量;例如使用main = print (intercalate " something " (reverse (map reverse list))) main = print (intercalate " something " ((reverse . map reverse) list)) main = print ((intercalate " something " . (reverse . map reverse)) list) main = (print . (intercalate " something " . (reverse . map reverse))) list作为索引有时也可以。

Ruby - 从增加长度的整数中分离出前两位数字

3 个答案: