Unpacking first dimension of NumPy array into pyplot.plot

Question

I have five sets of x,y data I'd like to plot in a single plt.plot() command by unwrapping the first dimension only of my array (of shape (5,2,500). If I try:

plt.plot(*arr)

I get the error

ValueError: third arg must be a format string

but if I plot by sending the x,y pairs separately, it works. e.g. for three lines:

plt.plot(arr[0][0], arr[0][1], arr[1][0], arr[1][1], arr[2][0], arr[2][1])

How can I unpack the first dimension only into the argument list for pt.plot?

I don't have time to write a complete answer right now. So i add this here, maybe someone else can make a complete answer from it. This seems to do what you're looking for plt.plot(arr[:,0,:].T, arr[:,1,:].T) — M4rtini
– M4rtini, Commented Jan 12, 2016 at 14:17

MB-F · Accepted Answer · 2016-01-12 14:28:43Z

2

plt.plot(*arr)

is equivalent to

plt.plot(arr[0], arr[1], arr[2], arr[3], arr[4])

That's why it does not work.

As @M4rtini wrote in their comment, you can do plt.plot(arr[:,0,:].T, arr[:,1,:].T).

plt.plot(X, Y) creates a separate plot for each column in X and Y. Thus, arr[:, 0] and arr[:, 1] extract blocks of x and y coordinates, and .T transposes the blocks so that the first dimension goes into the columns.

edited Jan 12, 2016 at 14:28

answered Jan 12, 2016 at 14:22

MB-F

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