How to add new buttons and call backs to a gui

Hi all: I have a matlab GUI for performing Principal Component Analysis (PCA). Sometimes it is necessary to remove an outlier from the dataset. The GUI was originally designed such that when you insert the outliers IDs, (eg 45), it will delete that sample 45, however, if sample 45 does not exist, there will be a prompt saying 'sample 45 does not exist'. I want to modify this GUI such that when the GUI identifies that sample 45 does not exist in the original data file, there will be a button telling me 'delete?' How do I go about adding the delete button and its callback to the existing matlab code (GUI). Any code ideas?

Thank you. Sorry for the long explanation

[Adam]

doc uicontrol

Just give it a parent, a position and a callback.