existField

Determine if a field exists at a specific location within a struct.

This function returns true if a field exists at a specific location within the struct. This is useful if you want to know if a field exists only within one position in the struct, especially for non-scalar structs. Use existField if you want to know about one specific location in a struct, e.g. if you want to know if a.b.c exists but don't care if a.c exists, and for non-scalar structs. This is in contrast to existing options such as hasfield and isfieldrecursive, which examine the struct as a whole with no specificity for one specific struct location, and also do not handle non-scalar fields.

existField Syntax:

boolean=existField(struct,path,varargin);
% Inputs:
% struct: The structure to look in (struct)
% path: The path name to the field to check for (char)
% varargin: Variables for dynamic path names (char) or dynamic indexing (numeric) 
%   NOTE: Must be in the same order that they appear in the struct path

% Outputs:
% boolean: true if the field exists at the specified location, false if not (boolean)

existField Examples:

% Create a sample structure
struct.a(1).b=1;
struct.b(1,2).c=1;
struct.d(2).e=1;
fldName='b'; % Dynamic field name
num=1; % Dynamic index

% Examples that return true.
existField(struct.a,'b'); % The same as the builtin isfield
existField(struct,'struct.a.b'); % Check a subfield within the struct by specifying its full location
existField(struct,'struct.d(2).e'); % Hard-coded vector indexing
existField(struct,'struct.d(num).e',num); % Dynamic vector indexing
existField(struct,'struct.b(num,2).c',num); % Mix of hard-coded & dynamic matrix indexing
existField(struct,'struct.(fldName)(1,2).c',fldName); % Dynamic field name with hard-coded indexing
existField(struct,'struct.(fldName)(num,2).c',fldName,num); % Dynamic field name and dynamic indexing

% Examples that return false.
existField(struct.b,'e'); % The same as the builtin isfield
existField(struct,'struct.b.e'); % Check a subfield within the struct by specifying its full location
existField(struct,'struct.d(3).e'); % Hard-coded vector indexing. size(struct.d,1)<3
existField(struct,'struct.d(num).e',3); % Dynamic vector indexing. size(struct.d,1)<3
existField(struct,'struct.b(num,2).c',3); % Mix of hard-coded & dynamic matrix indexing. size(struct.b,1)<3
existField(struct,'struct.(fldName)(3,2).c',fldName); % Dynamic field name with hard-coded indexing. size(struct.b,1)<3
existField(struct,'struct.(fldName)(3,num).c',fldName); % Dynamic field name and dynamic indexing. size(struct.b,1)<3

hasfield and isfieldrecursive do not handle non-scalar structs:

% Adapted from isfieldrecursive FileExchange description
myStructure.a(1).calibration1.left.fc = 1;
myStructure.a(2).calibration2.right.fc = 1;
myStructure.a(3).calibration3.centre.fc = 1;
% Returns false because it can't be indexed
isfieldRecursive(myStructure,'a','calibration3','centre')
% Returns true because index is specified
existField(myStructure,'myStructure.a(3).calibration3.centre')

% Adapted from hasfield FileExchange description
d.b.d.b(2).a.waldo = 'where?'
d.b.d.b(1).a.nowaldo='nowhere'
% Throws an error! Doesn't handle non-scalar structs
[x,L] = hasfield(d,'waldo')
% Returns true, as it should
existField(d,'d.c.d.b(2).a.waldo')
% Returns true and L=1 because it doesn't distinguish between fields of the same name at different levels
[x,L] = hasfield(d,'b')