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16.3 Applying a Function to an Array

Function File: arrayfun (func, a)
Function File: x = arrayfun (func, a)
Function File: x = arrayfun (func, a, b, …)
Function File: [x, y, …] = arrayfun (func, a, …)
Function File: arrayfun (…, "UniformOutput", val)
Function File: arrayfun (…, "ErrorHandler", errfunc)

Execute a function on each element of an array. This is useful for functions that do not accept array arguments. If the function does accept array arguments it is better to call the function directly.

The first input argument func can be a string, a function handle, an inline function or an anonymous function. The input argument a can be a logic array, a numeric array, a string array, a structure array or a cell array. By a call of the function arrayfun all elements of a are passed on to the named function func individually.

The named function can also take more than two input arguments, with the input arguments given as third input argument b, fourth input argument c, … If given more than one array input argument then all input arguments must have the same sizes, for example

 
arrayfun (@atan2, [1, 0], [0, 1])
⇒ ans = [1.5708   0.0000]

If the parameter val after a further string input argument "UniformOutput" is set true (the default), then the named function func must return a single element which then will be concatenated into the return value and is of type matrix. Otherwise, if that parameter is set to false, then the outputs are concatenated in a cell array. For example

 
arrayfun (@(x,y) x:y, "abc", "def", "UniformOutput", false)
⇒ ans =
{
  [1,1] = abcd
  [1,2] = bcde
  [1,3] = cdef
}

If more than one output arguments are given then the named function must return the number of return values that also are expected, for example

 
[A, B, C] = arrayfun (@find, [10; 0], "UniformOutput", false)
⇒
A =
{
  [1,1] =  1
  [2,1] = [](0x0)
}
B =
{
  [1,1] =  1
  [2,1] = [](0x0)
}
C =
{
  [1,1] =  10
  [2,1] = [](0x0)
}

If the parameter errfunc after a further string input argument "ErrorHandler" is another string, a function handle, an inline function or an anonymous function, then errfunc defines a function to call in the case that func generates an error. The definition of the function must be of the form

 
function […] = errfunc (s, …)

where there is an additional input argument to errfunc relative to func, given by s. This is a structure with the elements "identifier", "message" and "index", giving respectively the error identifier, the error message and the index of the array elements that caused the error. The size of the output argument of errfunc must have the same size as the output argument of func, otherwise a real error is thrown. For example

 
function y = ferr (s, x), y = "MyString"; endfunction
arrayfun (@str2num, [1234], \
          "UniformOutput", false, "ErrorHandler", @ferr)
⇒ ans =
{
 [1,1] = MyString
}

See also: cellfun, spfun, structfun.

Loadable Function: bsxfun (f, a, b)

Applies a binary function f element-wise to two matrix arguments a and b. The function f must be capable of accepting two column vector arguments of equal length, or one column vector argument and a scalar.

The dimensions of a and b must be equal or singleton. The singleton dimensions of the matrices will be expanded to the same dimensionality as the other matrix.

See also: arrayfun, cellfun.


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