python plot horizontal line for a range of values

Question

I am really new to python and trying to plot speed as a constant value for the distince from its current startpointinmeters to the next startpointinmeters, so speed is constant from the start to the end (next start).

For example, speed should be 13 for distance 0 to 27.82 and 15 from 27.82 to 40.12 and so on.

Any idea?

startpointinmeters speed
0.0     13.0
27.82   15.0
40.12   14.0
75.33   14.0
172.77  17.0
208.64  18.0
253.0   21.0
335.21  20.0
351.16  25.0
590.38  22.0
779.37  21.0
968.35  22.0
1220.66 20.0
1299.17 19.0
1318.32 14.0
1352.7  9.0

What is your current input? Seems that speed is there?

Tuan Anh Hoang-Vu
– Tuan Anh Hoang-Vu

2015-05-14 20:34:47 +00:00
Commented May 14, 2015 at 20:34 — Tuan Anh Hoang-Vu
– Tuan Anh Hoang-Vu, Commented May 14, 2015 at 20:34

Bas Swinckels · Accepted Answer · 2015-05-14 23:12:30Z

7

This can be done with the step function of Matplotlib:

import matplotlib.pyplot as plt

x = [0., 27.82, 40.12, 75.33, 172.77, 208.64, 253., 335.21, 351.16,
     590.38, 779.37, 968.35, 1220.66, 1299.17, 1318.32, 1352.7]
v = [13., 15., 14., 14., 17., 18., 21., 20., 25., 22., 21., 22., 20., 
     19., 14., 9.] 

plt.step(x, v, where='post')
plt.xlabel('Position [m]')
plt.ylabel('Speed [m/s]')
plt.show()

Result:

enter image description here

See this example for the difference between the different values for the 'where' argument. From your description it seems you want the 'post' option.

edited May 14, 2015 at 23:12

answered May 14, 2015 at 20:45

Bas Swinckels

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2 Comments

Jblasco Over a year ago

Neat! I didn't know plt.step :).

Kexin Xu Over a year ago

Does any know how to add grid based on the value of position?

Jblasco · Accepted Answer · 2015-05-14 20:43:45Z

0

You need to plot the points (0.0, 13.0), (27.82,13.0), (27.82,15.0), (40.12,15.0)... and continue like that till the end.

When you plot a line between (0.0, 13.0) and (27.82, 13.0) it will draw a flat line between 0 and 27.82, at the level of 13.0. Then, when the next point comes, the line goes from (27.82, 13.0) to (27.82, 15.0), meaning it goes up without going anywhere in the x axis. And so on.

In other words, you need to do a loop through all the values xi and yi, and pair them like: (x[i], y[i]), (x[i+1], y[i]) and so on...

answered May 14, 2015 at 20:43

Jblasco

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