Exist function returning 0 for a variable that definitely exists?

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Brendan Macklem
Brendan Macklem 2018-7-18
评论： Brendan Macklem 2018-7-18
I'm trying to use the 'exist' function to check whether a certain variable has been read in from a .csv file, as the existence of that variable defines the direction the rest of the code should take. This is what I have boils down to:
if exist('DATA.processedData.VTI_EX1048_09_CJC09', 'var')
CJCConfirm = 'Yes';
else
CJCConfirm = 'No';
end
(For reasons out of my control, the return has to be 'yes' or 'no'). However, even when running a data set where I know that DATA.processedData.VTI_EX1048_09_CJC09 exists (confirmed by putting it into the command window and seeing it returns a value), this:
exist DATA.processedData.VTI_EX1048_09_CJC09
still returns a 0. I've checked, and the exist function works fine with other variables in my workspace.
What do I need to do differently?

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James Tursa
James Tursa 2018-7-18
编辑：James Tursa 2018-7-18
Don't use exist() with struct field syntax. Only use it for variable names. E.g.,
>> a.f = 4
a =
f: 4
>> exist('a','var')
ans =
1
>> exist('a.f','var')
ans =
0
>> exist('a','var') && isfield(a,'f')
ans =
1
  2 个评论
Steven Lord
Steven Lord 2018-7-18
Also keep in mind that you can't specify multiple levels of indexing in one call to isfield.
a = struct('b', struct('c', 2));
abc = a.b.c % 2
check_bc = isfield(a, 'b.c') % false
check_b_then_c = isfield(a, 'b') && isfield(a.b, 'c') % true
The struct a does not have a field named b.c (and that would be an invalid field name, so it can't have a field with that name) but the struct stored in a.b does have a field named c.

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