inconsistency when comparing cell arrays with strings vs char array

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Ian
Ian 2019 年 3 月 8 日
コメント済み: Ian 2019 年 3 月 9 日
Why does matlab not compare strings & char arrays the same way in aggregate as it does individually?
>> type test_input.m
function test_input(varargin)
disp(strcmp(varargin,"abcd")); % try comparing against string "abcd"
disp(strcmp(varargin,'abcd')); % try comparing against char array 'abcd'...gets same result.
for i=1:length(varargin)
disp(strcmp(varargin{i},"abcd")) % try comparing individually, different result
end
end
>> test_input('abcd','efghi',"abcd")
1 0 0 % <-- match "abcd" with char array 'abcd', but mismatch on string "abcd"
1 0 0 % <-- also match 'abcd' with char array 'abcd', but mismatch on string "abcd"
1 % <-- match 'abcd' with string "abcd:
0
1 % <-- match "abcd" with "abcd". why is this different from aggregate compare????
>> test_input("abcd",'efghi','abcd')
0 0 1 % <-- (same results when switching input around...)
0 0 1
1
0
1
i.e., strcmp(...) doesn't match the input string "abcd" with either 'abcd' or "abcd" when comparing all elements of varargin at once, but does match the input char array 'abcd' with both "abcd" and 'abcd' when comparing in aggregate. However, it does match strings and char arrays properly when comparing individually.
This makes it an interesting challenge for testing for specific strings when the user could call my function with either string text or char array text?...

回答 (2 件)

Kevin Phung
Kevin Phung 2019 年 3 月 8 日
'abcd' is considered a 1v4 char.
"abcd" is considered a 1x1 string
  1 件のコメント
Ian
Ian 2019 年 3 月 8 日
編集済み: Ian 2019 年 3 月 8 日
Yes, but it actually considers 'abcd' and "abcd" as the same when comparing them individually, but does not consider the identical strings "abcd" and "abcd" as the same when comparing against the entire cell array.

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James Tursa
James Tursa 2019 年 3 月 8 日
編集済み: James Tursa 2019 年 3 月 8 日
This is a really good question. E.g.,
>> version
ans =
'9.4.0.813654 (R2018a)'
>> strcmp("abcd","abcd")
ans =
logical
1
>> strcmp({"abcd"},"abcd")
ans =
logical
0
>> strcmp('abcd','abcd')
ans =
logical
1
>> strcmp({'abcd'},'abcd')
ans =
logical
1
>> strcmp({'abcd',"abcd"},'abcd')
ans =
1×2 logical array
1 0
>> strcmp({'abcd',"abcd"},"abcd")
ans =
1×2 logical array
1 0
Not sure why the strcmp treatment of strings should be different when they are part of cell arrays. Maybe this needs to be posted to the TMW bug report system and see what they have to say about it.
As an aside, the ismember( ) function has limitations in this respect also. E.g.,
>> ismember({"abcd"},"abcd")
Error using ismember (line 76)
First argument must be a string array, character vector, or cell array of character vectors.
>> ismember({'abcd'},"abcd")
ans =
logical
1
  1 件のコメント
Ian
Ian 2019 年 3 月 9 日
Glad I'm not the only one puzzled by this. Am posting as TMW bug report, will update this when they respond.

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