## Sunday, September 5, 2021

### TI-Nspire CX II and TI-84 Plus CE: COUNTIF, SUMIF, AVERAGEIF

TI-Nspire CX II and TI-84 Plus CE:  COUNTIF, SUMIF, AVERAGEIF

Introduction

Three popular spreadsheet functions are operating on elements of a list contingent of a criteria.

Let L be a list of numerical data.

COUNTIF(L, criteria):   returns a count of all the elements that fit a criteria

SUMIF(L, criteria):  returns the sum of all the elements that fit a criteria

AVERAGEIF(L, criteria):  returns the arithmetic average of all the elements that fit a criteria

Example:

L = {0, 1, 2, 3, 4, 5, 6}

COUNTIF(L, "≥4") = 3.

Counts all the elements of L that are greater than or equal to 4.

SUMIF(L, "≥4") = 15

Sums all the element's of L that are greater than or equal to 4.

AVERAGEIF(L, "≥4") = 5

Returns the arithmetic average of L that are greater than or equal to 4.

Note that:

AVERAGEIF(L, criteria) = SUMIF(L, criteria) ÷ COUNTIF(L, criteria)

TI-Nspire CX II:  The functions countif and sumif

The TI-Nspire has two built in functions countif and sumif.  The averageif can easily be defined in the equation from the last section.

TI-84 Plus CE Programs:  LISTIF

The program LISTIF calculates all three functions COUNTIF, SUMIF, and AVERAGEIF.  There are two custom lists that are created as a result of this program:

List A:  The input list.

List B:  The list that meets the criteria.

To get the small "L" character, press [ 2nd ], [ stat ] (LIST), B* for the small L.   The small L must be the first character of your list name.  Once created, custom lists are shown under the LIST - NAMES menu.

Although I did not test this on previous calculators, this program should work on the TI-82, TI-83 family, and all of the TI-84 Plus family.

Program listing: