Normalization Normal forms

First Normal Form 1NF

No repeating columns or columns contain only a single value.


Second Normal Form 2NF

As per 1NF but each non PK value can be uniquely identified by the PK

Third Normal Form 3NF

As per 2NF but each no PK value can ONLY be identified by the PK

Comparison between SQL and Pandas

Comparison with SQL

VirtualBox command line. Removing innaccessable VMs change machine location

To delete virtual machines from the command line, first I removed the *.vbox *.vmdk files etc (basically the folder that these files are in).

Then;
VBoxManage list vms (this lists virtual machines)
VBoxManage unregistervm ********* (where *** is the number of the VM as shown by the previous command).

To change default location of VM's
vboxmanage setproperty machinefolder /path/to/directory/
Note use path in quotation marks if folder needs a space, example;
vboxmanage setproperty machinefolder "/var/VirtualBox VMs"

Mac add Open With to Right Click menu

Add OPEN WITH to Right click menu

1. Open Automator and select Service document type.
2. Select Files and Folders in the top Service receives selected menu
3. Search for and select the Open Finder Items action.
4. Now select TextEdit in Open with:
5. Save the service with a name you want to see in the menus

You can now find this by: 

• Right-clicking the file > Services

Renaming a file to include date

To rename a file to include the date in the filename use the following:

mv myfile.txt myfile_$(date + %d-$m-%Y).txt

This can be useful when creating backup files.

A script called by cron like the below might be useful.

#!/bin/bash
rm myfile_*.tar
tar -cf myfile.tar myfile.txt && mv myfile.tar myfile_$(date + %d-$m-%Y).tar