Excel's Formula - sisman

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Part IV: Array Formulas
The IF function creates a new array that consists of the row number of values from the Data
range that are equal to Value. Values from the Data range that aren’t equal to Value are replaced
with an empty string. The SMALL function works on this new array and returns the nth smallest
row number.
The formula returns #NUM! if the value is not found or if n exceeds the number of occurrences of
the value in the range.
Returning the longest text in a range
The following array formula displays the text string in a range (named Data) that has the most
characters. If multiple cells contain the longest text string, the first cell is returned.
{=INDEX(Data,MATCH(MAX(LEN(Data)),LEN(Data),FALSE),1)}
This formula works with two arrays, both of which contain the length of each item in the Data
range. The MAX function determines the largest value, which corresponds to the longest text
item. The MATCH function calculates the offset of the cell that contains the maximum length. The
INDEX function returns the contents of the cell containing the most characters. This function
works only if the Data range consists of a single column.
Determining whether a range contains valid values
You may have a list of items that you need to check against another list. For example, you may
import a list of part numbers into a range named MyList, and you want to ensure that all the part
numbers are valid. You can do so by comparing the items in the imported list to the items in a
master list of part numbers (named Master).
The following array formula returns TRUE if every item in the range named MyList is found in the
range named Master. Both ranges must consist of a single column, but they don’t need to contain
the same number of rows.
{=ISNA(MATCH(TRUE,ISNA(MATCH(MyList,Master,0)),0))}
The array formula that follows returns the number of invalid items. In other words, it returns the
number of items in MyList that do not appear in Master.
{=SUM(1*ISNA(MATCH(MyList,Master,0)))}
To return the first invalid item in MyList, use the following array formula:
{=INDEX(MyList,MATCH(TRUE,ISNA(MATCH(MyList,Master,0)),0))}