Why does the unique() function give an unexpected extra output here?

5 次查看（过去 30 天）
Can Atalay
Can Atalay 2021-10-17
编辑： dpb 2021-10-17
I'm trying to find the unique elements inside a string array (attached, "datestrings_of_problem_times.mat").
When I run this (after loading "datestrings_of_problem_times.mat") ;
[datestrings_of_interest, indices, b] = unique(datestrings_of_problem_times);
The output "datestrings_of_interest" (attached, "datestrings_of_interest.mat") has an empty string ( [""] ) as its first element, but there are no empty strings inside my initial string array.
And, the output "indices" (attached, "indices") has 50877 as its first element. But, my string array has 50876 elements in the first place. So, the unique function somehow checked whether the 50877th element of a 50876x10 string array was unique or not. What am I missing / how could I fix this?

请先登录，再回答此问题。

采纳的回答

dpb
dpb 2021-10-17
编辑：dpb 2021-10-17
>> load ..\Answers\datestrings_of_problem_times.mat
>> whos d*
Name Size Bytes Class Attributes
datestrings_of_problem_times 50876x10 27473136 string
>> datestrings_of_problem_times(1:10,:)
ans =
10×10 string array
"12/2017" "" "" "" "" "" "" "" "" ""
"12/2017" "" "" "" "" "" "" "" "" ""
"12/2017" "" "" "" "" "" "" "" "" ""
"12/2017" "" "" "" "" "" "" "" "" ""
"12/2017" "" "" "" "" "" "" "" "" ""
"12/2017" "" "" "" "" "" "" "" "" ""
"12/2017" "" "" "" "" "" "" "" "" ""
"12/2017" "" "" "" "" "" "" "" "" ""
"12/2017" "" "" "" "" "" "" "" "" ""
"12/2017" "" "" "" "" "" "" "" "" ""
>>
The problem is you have somehow created a 2D string array, the elements of which for columns 2:10 are all empty strings; ergo unique over the full array is correct to include the empty element as a unique string.
Using only the first column, one gets the expected result.
>> unique(s(:,1))
ans =
21×1 string array
"01/2018"
"02/2018"
"02/2020"
"02/2021"
"03/2019"
"03/2020"
"03/2021"
"04/2020"
"04/2021"
"05/2019"
"06/2018"
"06/2019"
"06/2020"
"07/2018"
"08/2019"
"10/2018"
"11/2018"
"11/2019"
"11/2020"
"12/2017"
"12/2020"
>>
We'd have to see the code that created the array to know how the 2D array came into existence, but that's where the symptoms arise.
  1 个评论
Can Atalay
Can Atalay 2021-10-17
Ooh this solved it. I initially didn't catch that I created something like
string_array = strings(50876,10)
and only filled the first column.
Thanks a bunch!

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Characters and Strings 的更多信息

标签

产品


版本

R2019a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by