Step plots

In [1]:

from plotnine import ggplot, aes, geom_step, geom_line, labs, theme, element_text
from plotnine.data import economics

geom_step() connects points using ‘steps’ instead of a line.

In [2]:

# inspect the data
economics.head()

	date	pce	pop	psavert	uempmed	unemploy
0	1967-07-01	507.4	198712	12.5	4.5	2944
1	1967-08-01	510.5	198911	12.5	4.7	2945
2	1967-09-01	516.3	199113	11.7	4.6	2958
3	1967-10-01	512.9	199311	12.5	4.9	3143
4	1967-11-01	518.1	199498	12.5	4.7	3066

Plot a step plot using geom_plot(). Notice from the first point the line travels vertically then horizontally:

In [3]:

(
    ggplot(
        economics.iloc[:20],  # filter for first twenty rows (dates) to make steps more visible
        aes("date", "unemploy"),
    )
    + geom_step()  # step plot
    + labs(x="date", y="unemployment (,000)")  # label x & y-axis
    + theme(axis_text_x=element_text(angle=45))  # rotate x-axis text for readability
)

You can see how geom_path() (shown in pink) differs from geom_line() (black):

In [4]:

(
    ggplot(economics.iloc[:20], aes("date", "unemploy"))
    + geom_step(
        colour="#ff69b4",  # plot geom_step as the first layer - colour pink
        alpha=0.5,  # line transparency
        size=2.5,
    )  # line thickness
    + geom_line()  # plot geom_line as the second layer
    + labs(x="date", y="unemployment (,000)")
    + theme(axis_text_x=element_text(angle=45))
)

Rather than a line that travels vertically then horizontally, this order can be switched by specifying direction='vh' within geom_step(). Below direction='vh' is shown in black with the default direction='hv' shown in pink:

In [5]:

(
    ggplot(economics.iloc[:20], aes("date", "unemploy"))
    + geom_step(
        colour="#ff69b4",  # plot geom_path with default direction as the first layer - colour pink
        linetype="dashed",  # line type
        size=2,  # line thickness
        alpha=0.5,
    )  # line transparency
    + geom_step(direction="vh")  # plot geom_path with step order reversed
    + labs(x="date", y="unemployment (,000)")
    + theme(axis_text_x=element_text(angle=45))
)