Other ways to do this here as well:

[https://superuser.com/questions/722461/how-can-you-remove-duplicates-from-bash-history][1]

Also

`sort ~/.bash_history | uniq -u`

or 
in vim text editor
[`:sort u`][2]

If some of the suggestions including the ones above don't work immediately. After running the code I do:

 history -c

to clear the history first then restore the no duplications version over it:

 cp temp.txt ~/.bash_history


 [1]: https://superuser.com/questions/722461/how-can-you-remove-duplicates-from-bash-history
 [2]: https://stackoverflow.com/a/29418407/3426192