Find a value in a field of a cell array of structures

Question

Having defined the GNU/Octave cell array

dict = 
{
  [1,1] =
    scalar structure containing the fields:
      id = integers
      vl = ... -2, -1, 0, 1, 2, ...
  [1,2] =
    scalar structure containing the fields:
      id = positive integers
      vl = 1, 2, 3, 4, ...
  [1,3] =
    scalar structure containing the fields:
      id = negative integers
      vl = -1, -2, -3, -4, ...
}

how to find (in Octave code, without looping!) the structs that have a given value in a field, say, those containing 'integer' in the id field, or -1 in the vl field.

Update: The command would operate like find(dict,'vl','-1'), returning 1, 3, or 1 0 1.

Answer 1

A possible implementation of the search function would look like:

function arrayvalues = findinfield(mycellarray, inputfield, outputfield, fieldvalue)

  positions = ~cellfun(@isempty, regexp({[mycellarray{:}].(inputfield)}, fieldvalue));
  arrayvalues = {[mycellarray{positions}].(outputfield)};

end

For an exact matching add ^ and $ to the beginning and end, respectively, of the regular expression.

Use cases:

findinfield(dict, "id", "vl", "integers")
ans = 
{
  [1,1] = ... -2, -1, 0, 1, 2, ...}
  [1,2] = 1, 2, 3, 4, ...}
  [1,3] = -1, -2, -3, -4, ...}
}

findinfield(dict, "id", "vl", "^integers$")
ans = 
{
  [1,1] = 1, 2, 3, 4, ...}
}

findinfield(dict, "id", "vl", "negative")
ans = 
{
  [1,1] = -1, -2, -3, -4, ...}
}