FUNCTION: argnanmin( arr )
Computes the minimum value of an array ignoring non-numeric values and returns the corresponding array indices.

@param {Array} arr - array of values
@returns {Array} array indices
function argnanmin( arr ) {
	if ( !Array.isArray( arr ) ) {
		throw new TypeError( 'argnanmin()::invalid input argument. Must provide an array.' );
	}
	var len = arr.length,
		min = Number.POSITIVE_INFINITY,
		idx = [],
		val;

	for ( var i = 0; i < len; i++ ) {
		val = arr[ i ];
		if ( typeof val !== 'number' || val !== val ) {
			continue;
		}
		if ( val < min ) {
			min = val;
			idx.length = 0;
			idx.push( i );
		}
		else if ( val === min ) {
			idx.push( i );
		}
	}
	return idx;
}