How to detect missing values in a string cell array

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.

[Walter Roberson]

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

[Stephen23]

"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)

Answer 1

[Walter Roberson]

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

[Leon]

Exactly what I'm looking for. Thank you so much.

[Image Analyst]

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]

@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]}