Data cleaning: Difference between revisions

=== deduplicate ===

* EXCEL: Data Tools -> Remove Duplicates: [https://support.office.com/en-us/article/Filter-for-unique-values-or-remove-duplicate-values-d6549cf0-357a-4acf-9df5-ca507915b704 Filter for unique values or remove duplicate values] {{access | date = 2015-10-20}}

* PHP: [http://php.net/manual/en/function.array-unique.php PHP: array_unique], [http://php.net/manual/en/function.array-intersect.php PHP: array_intersect]

* MySQL:  

** [http://www.mysqltutorial.org/mysql-distinct.aspx MySQL DISTINCT - Eliminate Duplicate Rows in a Result Set]. Using {{kbd | key =GROUP_CONCAT}} to handle the multiple columns<ref>[http://stackoverflow.com/questions/12188027/mysql-select-distinct-multiple-columns sql - MySQL SELECT DISTINCT multiple columns - Stack Overflow]</ref>

** [http://www.w3schools.com/sql/sql_unique.asp SQL UNIQUE Constraint] "Note that you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table." Quoted from w3schools webpage.

** "{{kbd | key = UNION}} removes duplicates, whereas {{kbd | key = UNION ALL}} does not." source: [http://stackoverflow.com/questions/49925/what-is-the-difference-between-union-and-union-all sql - What is the difference between UNION and UNION ALL? - Stack Overflow]

* [http://www.gnu.org/software/coreutils/manual/html_node/sort-invocation.html GNU Coreutils: sort invocation] ex: {{kbd | key=sort -us -o output_unique.file input.file}} to remove duplicate lines in a large text file (GB)<ref>[http://unix.stackexchange.com/questions/19641/how-to-remove-duplicate-lines-in-a-large-multi-gb-textfile linux - How to remove duplicate lines in a large multi-GB textfile? - Unix & Linux Stack Exchange]</ref> OS: {{Linux}}, cygwin of {{Win}}

* Google spreadsheet add-on: [https://www.ablebits.com/google-sheets-add-ons/remove-duplicates/howto.php Remove Duplicates for Google Sheets help]