How to detect missing values in a string cell array

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Leon
Leon 2025-3-8
评论： Walter Roberson 2025-3-9
I have a cell array A like the below:
Columns 1 through 4
{'NAME'} {'STNNBR'} {[<missing>]} {'SAMPNO'} .
I tried to find the location of the missing value by doing the below:
B = ismissing(A)
Why is the value of B zero for all of them? Shouldn't the answer be: 0 0 1 0?
Columns 1 through 4
0 0 0 0
What is the correct way to write this code? Thanks.
  2 个评论
Walter Roberson
Walter Roberson 2025-3-9

Ah, but the missing element is not a character vector, so this is not a cell array of character vectors

Stephen23
Stephen23 2025-3-9
"Why is the value of B zero for all of them? Shouldn't the answer be: 0 0 1 0?"
The ISMISSING documentation states that for a cell array of character vector ISMISSING returns TRUE for empty character vectors: "Missing values are defined according to the data type of A ... {''} — cell of character vectors"
Your data do NOT match this requirement.
Source: https://www.mathworks.com/help/matlab/ref/ismissing.html#description
"What is the correct way to write this code?"
Use a STRING array:
A = ["NAME", "STNNBR", missing, "SAMPNO"]
ismissing(A)

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Walter Roberson
Walter Roberson 2025-3-8
Ran in:
You are applying ismissing() to a cell array. That is the same thing as calling
[ismissing(A(1)), ismissing(A(2)), ismissing(A(3)), ismissing(A(4))]
A(1), A(2), A(3), A(4) are all cells -- and the cells are not missing.
You should probably be using a string array rather than a cell array,
A = ["NAME", "STNNBR", nan, "SAMPNO"]
A = 1x4 string array
"NAME" "STNNBR" <missing> "SAMPNO"
ismissing(A)
ans = 1x4 logical array
0 0 1 0
but if you insist on using a cell array then you should have something more like
B = {'NAME', 'STNNBR', string(nan), 'SAMPNO'};
cellfun(@(X)any(ismissing(X),'all'), B)
ans = 1x4 logical array
0 0 1 0
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Image Analyst
Image Analyst 2025-3-9
I always get confused as to when I should use ismissing or isempty. It seems no matter which one I use first, it's always the second one that I should use. Any intuitive rule of thumb as to use the right one?
Walter Roberson
Walter Roberson 2025-3-9
Ran in:
@Image Analyst
isempty: There is no data here.
ismissing(): There is data here, but some of it is marked as being invalid.
if isempty([]); disp('empty'); else; disp('not empty'); end
empty
if ismissing([]); disp('missing'); else; disp('not missing'); end
not missing
C = {'ab', [1 2 missing], [], missing, ["cd", missing, "ef"]}
C = 1x5 cell array
{'ab'} {[1 2 NaN]} {0x0 double} {[<missing>]} {["cd" <missing> "ef"]}
cellfun(@isempty, C, 'uniform', 0)
ans = 1x5 cell array
{[0]} {[0]} {[1]} {[0]} {[0]}
cellfun(@ismissing, C, 'uniform', 0)
ans = 1x5 cell array
{[0 0]} {[0 0 1]} {0x0 logical} {[1]} {[0 1 0]}

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