Why is 211 used in plt.subplot(211)

Question

In the pyplot documentation I saw

plt.subplt(211) which is identical to subplot(2, 1, 1)

I've also seen 211 being used elsewhere. Why specifically are those numbers being used as opposed to other ones?

Answer 1

plt.subplot takes three arguments, the number of rows (nrows), the number of columns (ncols) and the plot number. Using the 3-digit code is a convenience function provided for when nrows, ncols and plot_number are all <10.

So, 211 is equivalent to nrows=2, ncols=1, plot_number=1.

From the docs:

Return a subplot axes positioned by the given grid definition.

Typical call signature:

subplot(nrows, ncols, plot_number) 

Where nrows and ncols are used to notionally split the figure into nrows * ncols sub-axes, and plot_number is used to identify the particular subplot that this function is to create within the notional grid. plot_number starts at 1, increments across rows first and has a maximum of nrows * ncols.

In the case when nrows, ncols and plot_number are all less than 10, a convenience exists, such that the a 3 digit number can be given instead, where the hundreds represent nrows, the tens represent ncols and the units represent plot_number. For instance:

subplot(211)

produces a subaxes in a figure which represents the top plot (i.e. the first) in a 2 row by 1 column notional grid (no grid actually exists, but conceptually this is how the returned subplot has been positioned).