count NO of values from a column base on same value of anoth

1                                          1

2                                           1

3                                            1

2                                            1

1 is for absent

2 is for Leave

3 for MEdical

i have a dropdown list of sector in the form ,i want that when user click on any dropdown list each an event is fire that return no of absent leave,medical in to the textbox of the form.

txt.absent.text = sectorAbsent.TOSTRING();