public static boolean isSubIndex(FormIndex parent, FormIndex child) {
if (child.equals(parent)) {
return true;
} else {
if (parent == null) {
return false;
}
return isSubIndex(parent.nextLevel, child);
}
}
/**
* Takes in a form index which is a subset of this index, and returns the total difference between
* them. This is useful for stepping up the level of index specificty. If the subIndex is not a
* valid subIndex of this index, null is returned. Since the FormIndex represented by null is
* always a subset, if null is passed in as a subIndex, the full index is returned
*
* <p>For example: Indices a = 1_0,2,1,3 b = 1,3
*
* <p>a.diff(b) = 1_0,2
*
* @param subIndex
* @return
*/
public FormIndex diff(FormIndex subIndex) {
if (subIndex == null) {
return this;
}
if (!isSubIndex(this, subIndex)) {
return null;
}
if (subIndex.equals(this)) {
return null;
}
return new FormIndex(nextLevel.diff(subIndex), this.snip());
}