Search 如何在八度的单元格数组(字符串)中排序并高效地查找元素?
是否有此功能的内置功能?是检查此项: GNU倍频程在线性时间内搜索字符串单元格数组Search 如何在八度的单元格数组(字符串)中排序并高效地查找元素?,search,sorting,find,octave,cell-array,Search,Sorting,Find,Octave,Cell Array,是否有此功能的内置功能?是检查此项: GNU倍频程在线性时间内搜索字符串单元格数组O(n): 另一个答案是cellidx,它按八度折旧,它仍然运行,但他们说使用ismember,如下所示: %linear time string index search. a = ["hello"; "unsorted"; "world"; "moobar"] b = cellstr(a) %b = %{ % [1,1] = hello % [2,1] = unsorted % [3,1] = world
O(n)
:
另一个答案是cellidx
,它按八度折旧,它仍然运行,但他们说使用ismember
,如下所示:
%linear time string index search.
a = ["hello"; "unsorted"; "world"; "moobar"]
b = cellstr(a)
%b =
%{
% [1,1] = hello
% [2,1] = unsorted
% [3,1] = world
% [4,1] = moobar
%}
find(ismember(b, 'world')) %returns 3
“世界”位于索引槽3中。这是一个昂贵的过程,因为无论是否找到它,它都必须遍历所有元素
若要实现a,则需要对列表进行预排序,然后可以使用二进制搜索:
如果单元格数组已排序,则可以执行O(log-n)
最坏情况:
不要羞于使用此dob的管道胶带,它是将装置连接在一起的唯一工具。cellidx解决方案不符合OP的效率要求,因此已被弃用(如
帮助cellidx
所述)
Håvard Geithus在一篇评论中建议在排序的单元格字符串数组上使用lookup()函数,这比cellidx的效率要高得多。不过,它仍然是一种二进制搜索,而大多数现代语言(甚至许多已有20年历史的语言)让我们能够轻松访问关联数组,这将是一种更好的方法
虽然Octave显然没有关联的数组,但解释器对Octave的变量(包括结构)有效地使用了数组,因此您可以让我们了解它,如下所述:
建议使用javaObject(“java.util.Hashtable”)。这将带来一些设置开销,但如果您经常使用它,这将是一个性能胜利。在C或C++中的某些图书馆中链接可能是可行的吗?但一定要考虑这是否是一个可维护的选项
注意:我对八度音阶比较陌生,在自己研究的过程中写下这篇文章(这就是我在这里结束的原因)。我还没有对这些技术的效率进行测试,虽然我对底层算法有相当的了解,但我可能对倍频程中的实际效率做出了不合理的假设。效果很好。不需要排序。如果未找到,则返回
0
。我想知道效率…这是暴力搜索吗?看起来是的。如果使用“which”函数并传递函数名,它将指向源文件。在本例中,“哪个cellidx”。如果您查看源代码,您会发现它确实执行了暴力搜索。请参阅我的答案(在问题提出很久之后添加)了解非暴力搜索选项。太糟糕了,但是cellidx被弃用(为什么?),并在Octave 3.8中删除了。给定一个按字典顺序排序的单元格数组,您可以使用Octave中的函数“lookup”执行二进制搜索。现在剩下的就是排序;)
%linear time string index search.
a = ["hello"; "unsorted"; "world"; "moobar"]
b = cellstr(a)
%b =
%{
% [1,1] = hello
% [2,1] = unsorted
% [3,1] = world
% [4,1] = moobar
%}
find(ismember(b, 'world')) %returns 3
function i = binsearch(array, val, low, high)
%binary search algorithm for numerics, Usage:
%myarray = [ 30, 40, 50.15 ]; %already sorted list
%binsearch(myarray, 30, 1, 3) %item 30 is in slot 1
if ( high < low )
i = 0;
else
mid = floor((low + high) / 2);
if ( array(mid) > val )
i = binsearch(array, val, low, mid-1);
elseif ( array(mid) < val )
i = binsearch(array, val, mid+1, high);
else
i = mid;
endif
endif
endfunction
function i = binsearch_str(array, val, low, high)
% binary search for strings, usage:
%myarray2 = [ "abc"; "def"; "ghi"]; #already sorted list
%binsearch_str(myarray2, "abc", 1, 3) #item abc is in slot 1
if ( high < low )
i = 0;
else
mid = floor((low + high) / 2);
if ( mystrcmp(array(mid, [1:end]), val) == 1 )
i = binsearch(array, val, low, mid-1);
elseif ( mystrcmp(array(mid, [1:end]), val) == -1 )
i = binsearch_str(array, val, mid+1, high);
else
i = mid;
endif
endif
endfunction
function ret = mystrcmp(a, b)
%this function is just an octave string compare, it's exactly like
%strcmp(str1,str2) in C, or java.lang.String.compareTo(...) in Java.
%returns 1 if string a > b
%returns 0 if string a == b
%return -1 if string a < b
letters_gt = gt(a, b); %list of boolean a > b
letters_lt = lt(a, b); %list of boolean a < b
ret = 0;
%octave makes us roll our own string compare because
%strings are arrays of numerics
len = length(letters_gt);
for i = 1:len
if letters_gt(i) > letters_lt(i)
ret = 1;
return
elseif letters_gt(i) < letters_lt(i)
ret = -1;
return
endif
end;
endfunction
%Assuming that myarray is already sorted, (it must be for binary
%search to finish in logarithmic time `O(log-n))` worst case, then do
myarray = [ 30, 40, 50.15 ]; %already sorted list
binsearch(myarray, 30, 1, 3) %item 30 is in slot 1
binsearch(myarray, 40, 1, 3) %item 40 is in slot 2
binsearch(myarray, 50, 1, 3) %50 does not exist so return 0
binsearch(myarray, 50.15, 1, 3) %50.15 is in slot 3
%same but for strings:
myarray2 = [ "abc"; "def"; "ghi"]; %already sorted list
binsearch_str(myarray2, "abc", 1, 3) %item abc is in slot 1
binsearch_str(myarray2, "def", 1, 3) %item def is in slot 2
binsearch_str(myarray2, "zzz", 1, 3) %zzz does not exist so return 0
binsearch_str(myarray2, "ghi", 1, 3) %item ghi is in slot 3
myarray = [ 9, 40, -3, 3.14, 20 ]; %not sorted list
myarray = sort(myarray)
myarray2 = [ "the"; "cat"; "sat"; "on"; "the"; "mat"]; %not sorted list
myarray2 = sortrows(myarray2)
Built-in Function: struct ("field", value, "field", value,...)
Built-in Function: isstruct (expr)
Built-in Function: rmfield (s, f)
Function File: [k1,..., v1] = setfield (s, k1, v1,...)
Function File: [t, p] = orderfields (s1, s2)
Built-in Function: fieldnames (struct)
Built-in Function: isfield (expr, name)
Function File: [v1,...] = getfield (s, key,...)
Function File: substruct (type, subs,...)