A first project in R / UK income tax graphs

The UK income tax system has a progressive tax rate that gets higher as your income is higher. However it has a few quirks. I've been meaning to graph the effective rates, and today I felt like learning a bit more R to do it. I've included income related student loan repayments and National Insurance because they are, to some extent, income-tax-like.

The code at https://github.com/benclifford/r-income-tax can generate the following three graphs:

Marginal income tax rates, coloured by component, for varying income:

Total tax, for varying income:

Fraction of income taken as tax, for varying income:

google chart venn diagram of disk usage

This compares disk usage of a backup I made of /home two years ago with one made this month. There's a lot of overlap - more than I expected.

Method: creating the second backup, I used rsync with --link-dest specified; for measuring, I used du -hsc old new; du -hsc new old. The size of the overlap is the size of new given by the second du minus the size of new given by the first du.

I'm trying to figure out ways of showing overlapping disk usage for more than two or three rsync trees created in this way (for example, to visualise monthly, weekly and daily backups over a long time period)