如何使用Ruby交換矩陣中的列和行

Question

我想要做的就是使用while循環交換matrix[i][j]和matrix[j][i]。爲什麼這不起作用？

def my_transpose(matrix) 

    new_matrix = [] 

    i = 0 
    j = 0 

    while i < matrix.size 
    new_matrix[i] = [] 
    while j < matrix.size 
     new_matrix[i] << matrix[j][i] 
     j += 1 
    end 
    i += 1 
    end 

    return new_matrix 
end 

如果我喜歡的東西

[ 
[1,2,3], 
[1,2,3], 
[1,2,3] 
] 

它只是返回1,1,1運行此。我如何獲得它返回1,1,1; 2,2,2; 3,3,3？

Answer 1

的i環路內移動j = 0

def my_transpose(matrix) 

    new_matrix = [] 

    i = 0 


    while i < matrix.size 
    new_matrix[i] = [] 
    j = 0 # move this here 
    while j < matrix.size 
     new_matrix[i] << matrix[j][i] 
     j += 1 
    end 
    i += 1 
    end 

    return new_matrix 
end 

如果j沒有重置爲0每i環路，則它不會進入j循環，除了第一次：

i = 0 
j = 0 
# Enter i loop 
new_matrix[0] = [] 
# Enter j loop 
    new_matrix[0] << matrix[0][0] 
    j += 1 #=> 1 

    new_matrix[0] << matrix[1][0] 
    j += 1 #=> 2 

    new_matrix[0] << matrix[2][0] 
    j += 1 #=> 3 
# Exit j loop 
i += 1 #=> 1 

new_matrix[1] = [] 
# Does not enter j loop as j = 3 > matrix.size 
i += 1 #=> 2 

new_matrix[2] = [] 
# Does not enter j loop as j = 3 > matrix.size 
i += 1 #=> 3 
# Exit i loop 

Answer 2

如果您問題是如何交換矩陣中的列和行與Ruby，答案是使用內置的Array#transpose

a = [ 
[1,2,3], 
[1,2,3], 
[1,2,3] 
] 
#=> [[1, 2, 3], [1, 2, 3], [1, 2, 3]] 
a.transpose 
#=> [[1, 1, 1], [2, 2, 2], [3, 3, 3]] 

Answer 3

您可以對此使用並行分配，例如， a,b = b,a。作爲一個方面說明，while循環在Ruby中很少使用，因此將它視爲一個新手。更類似Ruby的方法是使用像times,upto,downto等的枚舉數，它將很方便地提供指數i和j作爲循環變量。當你將這些方法存儲在Array類中時，你可以節省一次又一次地輸入matrix，因爲你已經在課堂上了。此外，首先編寫一個增變器方法（改變原始對象，通常在方法名稱末尾通常用砰砰聲!表示），然後編寫一個額外的非增變器方法，該方法簡單地調用複製器上的增變器。這是我會怎麼寫代碼：

class Array 
    def my_transpose! 
    size.times do |i| 
     0.upto(i) do |j|         # iterate only through lower half 
     self[i][j], self[j][i] = self[j][i], self[i][j] # swap rows and cols 
     end 
    end 
    self             # return the array itself 
    end 

    def my_transpose 
    dup.map(&:dup).my_transpose!       # inner arrays are dup'ed, too 
    end 
end 

有趣的是，Ruby的內置transpose不能作爲賦值函數。以下是如何使用上面的代碼：

a = [[1, 2, 3], [1, 2, 3], [1, 2, 3]] 

a.my_transpose!      # mutator 
#=> [[1, 1, 1], [2, 2, 2], [3, 3, 3]] 

a 
#=> [[1, 1, 1], [2, 2, 2], [3, 3, 3]] # note that a changed 

a.my_transpose! 
#=> [[1, 2, 3], [1, 2, 3], [1, 2, 3]] 

a 
#=> [[1, 2, 3], [1, 2, 3], [1, 2, 3]] # a is back to its original state 

a.my_transpose       # non-mutator 
#=> [[1, 1, 1], [2, 2, 2], [3, 3, 3]] 

a 
#=> [[1, 2, 3], [1, 2, 3], [1, 2, 3]] # note that a did not change