The 2 Most Important
Excel Functions AND
Formulas
SUMPRODUCT
AND
INDEX/MATCH

Lesson 5: Excel Spreadsheets Information Functions (17)
In annex 5 you have found a description of all 17 Excel functions in the "Information" category. Below is the list of the 2 most useful ones. See more on the very powerful ISERROR fonction.
Functions 
What it Does 
ISERROR 
Returns TRUE if the value is any
error value 
CELL 
Returns information about the
formatting, location, or contents of a cell 
Examples of Basic Information Formulas
CELL, MID, FIND
If you want the name and path of the
active spreadsheet to be entered automatically in
a cell, use the formula: =CELL("filename" )
if you want only the filename use
:
=MID(CELL("filename" ,A1),FIND("[" ,CELL("filename" ,A1))+1,FIND("]" ,CELL("filename" ,A1))FIND("[" ,CELL("filename",A1))1)
ISERROR/ISNA
When a formula refers to a cell in
which you have another formula, always use the
ISERROR function to avoid trashing the last
formula with a " #DIV/0" or a " #VALUE" or a
" #N/A" . =IF(ISERROR(B1/A1),"",(B1/A1))
if the value of cell A1 is 0, the cell in which you have put the
above formula will be empty and not carry a value of #DIV/0. =IF(ISERROR(B1/A1),0,(B1/A1))
if the value of cell A1 is 0, the value of the cell in which you have put the
above formula will be 0 and not #DIV/0.
I also use the ISERROR rather then
the ISNA function when I work with
INDEX/MATCH.
IF, ISNUM, LEFT and MID
In UK all postal codes start by a prefix of one or two letters. My correspondent wanted a formula to extract the prefixes so he could make a list of them. With the postal codes in column one the following formula in column 2 would do the job. =IF(ISNUMBER(MID(A1,2,1)*1),LEFT(A1,1),LEFT(A1,2)) Depending
on the number of characters in the prefix the formula should return the first character from the left or the first 2 characters from the left: LEFT(A1,1) or LEFT(A1,2) Before any of these solutions is applied we must check if there are one or two letters at the beginning of the postal code. To do so we will check if the second character MID(A1,2,1) is a number. The problem here is that any character from a text string is consider as a letter by Excel. Postal codes, serial numbers and others that include a letter or are formatted as text are text by nature . So we multiply the second character by 1. If the character is a digit to begin with it becomes a number but if it is a letter it doesn't: ISNUMBER(MID(A1,2,1)*1).
