Remove duplicates within same month or year
The array formula in cell B15 extracts dates from B4:B12 if it is not a duplicate item in the same month and year.
Array formula in B15:
To enter an array formula, type the formula in a cell then press and hold CTRL + SHIFT simultaneously, now press Enter once. Release all keys.
The formula bar now shows the formula with a beginning and ending curly bracket telling you that you entered the formula successfully. Don't enter the curly brackets yourself.
Array formula in C15:
Explaining formula in cell B15
Step 1 - Concatenate year, month and item value
The YEAR function returns the year of an Excel date, the MONTH function returns the MONTH of an Excel date.
YEAR($B$4:$B$12)&"-"&MONTH($B$4:$B$12)&"-"&$C$4:$C$12
becomes
YEAR({40183; 40184; 40185; 40186; 40218; 40188; 40220; 40190; 40556})&"-"&MONTH({40183; 40184; 40185; 40186; 40218; 40188; 40220; 40190; 40556})&"-"&{1124; 1126; 1131; 1126; 1126; 1160; 1126; 1155; 1155}
The & ampersand sign lets you concatenate values, in this case, row-wise.
YEAR({40183; 40184; 40185; 40186; 40218; 40188; 40220; 40190; 40556})&"-"&MONTH({40183; 40184; 40185; 40186; 40218; 40188; 40220; 40190; 40556})&"-"&{1124; 1126; 1131; 1126; 1126; 1160; 1126; 1155; 1155}
returns
{"2010-1-1124"; "2010-1-1126"; "2010-1-1131"; "2010-1-1126"; "2010-2-1126"; "2010-1-1160"; "2010-2-1126"; "2010-1-1155"; "2011-1-1155"}
Step 2 - Match concatenated values to identify duplicates
The MATCH function finds the relative position of a value in an array or cell range.
MATCH(YEAR($B$4:$B$12)&"-"& MONTH($B$4:$B$12)&"-"&$C$4:$C$12, YEAR($B$4:$B$12)& "-"&MONTH($B$4:$B$12)& "-"&$C$4:$C$12, 0)
becomes
MATCH{"2010-1-1124"; "2010-1-1126"; "2010-1-1131"; "2010-1-1126"; "2010-2-1126"; "2010-1-1160"; "2010-2-1126"; "2010-1-1155"; "2011-1-1155"}, {"2010-1-1124"; "2010-1-1126"; "2010-1-1131"; "2010-1-1126"; "2010-2-1126"; "2010-1-1160"; "2010-2-1126"; "2010-1-1155"; "2011-1-1155"}, 0)
and returns
{1; 2; 3; 2; 5; 6; 5; 8; 9}
Step 3 - Compare value to sequence
If number is equal to corresponding number in sequence the logical expression returns TRUE.
MATCH(YEAR($B$4:$B$12)&"-"& MONTH($B$4:$B$12)&"-"& $C$4:$C$12,YEAR($B$4:$B$12)&"-"& MONTH($B$4:$B$12)&"-"& $C$4:$C$12,0)=MATCH(ROW($B$4:$B$12), ROW($B$4:$B$12))
becomes
{1; 2; 3; 2; 5; 6; 5; 8; 9}=MATCH(ROW($B$4:$B$12), ROW($B$4:$B$12))
becomes
{1; 2; 3; 2; 5; 6; 5; 8; 9}={1;2;3;4;5;6;7;8;9}
and returns
{TRUE; TRUE; TRUE; FALSE; TRUE; TRUE; FALSE; TRUE; TRUE}
Step 4 - Replace TRUE with corresponding row number
The IF function has three arguments, the first one must be a logical expression. If the expression evaluates to TRUE then one thing happens (argument 2) and if FALSE another thing happens (argument 3).
IF(MATCH(YEAR($B$4:$B$12)&"-"&MONTH($B$4:$B$12)&"-"&$C$4:$C$12, YEAR($B$4:$B$12)&"-"&MONTH($B$4:$B$12)&"-"&$C$4:$C$12, 0)=MATCH(ROW($B$4:$B$12), ROW($B$4:$B$12)), MATCH(ROW($B$4:$B$12), ROW($B$4:$B$12)), "")
becomes
IF({TRUE; TRUE; TRUE; FALSE; TRUE; TRUE; FALSE; TRUE; TRUE}=MATCH(ROW($B$4:$B$12), ROW($B$4:$B$12)), MATCH(ROW($B$4:$B$12), ROW($B$4:$B$12)), "")
becomes
IF({TRUE; TRUE; TRUE; FALSE; TRUE; TRUE; FALSE; TRUE; TRUE}, {1;2;3;4;5;6;7;8;9}, "")
and returns
{1;2;3;"";5;6;"";8;9}.
Step 5 - Extract k-th smallest row number
To be able to return a new value in a cell each I use the SMALL function to filter column numbers from smallest to largest.
The ROWS function keeps track of the numbers based on an expanding cell reference. It will expand as the formula is copied to the cells below.
SMALL(IF(MATCH(YEAR($B$4:$B$12)&"-"&MONTH($B$4:$B$12)&"-"&$C$4:$C$12, YEAR($B$4:$B$12)&"-"&MONTH($B$4:$B$12)&"-"&$C$4:$C$12, 0)=MATCH(ROW($B$4:$B$12), ROW($B$4:$B$12)), MATCH(ROW($B$4:$B$12), ROW($B$4:$B$12)), ""), ROWS($A$1:A1))
becomes
SMALL({1;2;3;"";5;6;"";8;9}, ROWS($A$1:A1))
becomes
SMALL({1;2;3;"";5;6;"";8;9}, 1)
and returns 1.
Step 6 - Get value
The INDEX function returns a value based on a cell reference and column/row numbers.
INDEX($C$4:$C$12, SMALL(IF(MATCH(YEAR($B$4:$B$12)&"-"&MONTH($B$4:$B$12)&"-"&$C$4:$C$12, YEAR($B$4:$B$12)&"-"&MONTH($B$4:$B$12)&"-"&$C$4:$C$12, 0)=MATCH(ROW($B$4:$B$12), ROW($B$4:$B$12)), MATCH(ROW($B$4:$B$12), ROW($B$4:$B$12)), ""), ROWS($A$1:A1)))
becomes
INDEX($C$4:$C$12, 1)
and returns 1/5/2010 in cell B15.
Get Excel *.xlsx file
Remove-duplicates-in-same-month.xlsx
Remove duplicates within same year in excel
Array formula in B38:
Array formula in C38:
Get excel sample file for this article.
Remove-duplicates-in-same-month.xls
(Excel 97-2003 Workbook *.xls)
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2 Responses to “Remove duplicates within same month or year”
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Hi,
I was looking for a formula to remove duplicates within the same month and found your website. I think that your formula is really useful but when I try to apply it (I also tried with your sample), unfortunately I don't get any results and Excel gives me the "Value!" error. I also checked the format (columns for date and number)but it did not work. Do you know maybe more?
Kind regards.
I am experiencing the same issue that Amanda experiencing. The formula doesn't seem to work as written with your sample data. Can you provide a working sample in an excel file? Thank you.