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Very Confusing Float64MultiArray Error [closed]

asked 2022-12-15 05:30:58 -0500

distro
167 ●45 ●78 ●99

updated 2022-12-15 11:48:10 -0500

I get rospy.exceptions.ROSSerializationException: field data[] must be float type in terminal When I rostopic echo a topic recieving Float64MultiArray message. This is a snippet of my python code:

M = Float64MultiArray()
Tab=np.zeros((11521,10))
Values in Tab are manipulated,some are int, some are float.
M.data=(Tab.astype(float)).tolist()
pub.publish(M)

I don't get it, M.data is of type float. is Tab too big?

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Closed for the following reason the question is answered, right answer was accepted by distro
close date 2022-12-28 02:44:28.811739

Comments

Did you try creating the array by setting explicitly the type: Tab=np.zeros((11521,10),dtype=np.float64)?

AlessioParmeggiani ( 2022-12-15 14:56:05 -0500 )edit

@AlessioParmeggiani This still gives the same error

distro ( 2022-12-15 20:23:38 -0500 )edit

1 Answer

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answered 2022-12-18 10:20:30 -0500

Mike Scheutzow
4918 ●2 ●430 ●45

The .tolist() call is not doing what you think it is. If you want to flatten a 2d np.ndarray to a 1d list, use the ravel() method of ndarray.

M.data = Tab.astype(float).ravel()

For a good discussion, see:

https://stackoverflow.com/questions/2...

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Comments

@Mike Scheutzow This flattens all elements to a list like [x y z d]. I want to publish this [ [x y],[z d] ]. Maybe it's not possible?

distro ( 2022-12-18 13:45:14 -0500 )edit

You can easily adapt it in a few lines though, why is it a problem? Flatten it to 1D list, then create a 2D list with np.reshape

ljaniec ( 2022-12-18 15:20:07 -0500 )edit

@ljaniec "facepalm" thanks! I'll try that

distro ( 2022-12-18 17:22:41 -0500 )edit

I want to publish this [ [x y],[z d] ]

No, that is not possible with this message. From the message definition: data must be a 1d array of float64.

Mike Scheutzow ( 2022-12-19 08:21:34 -0500 )edit

Good note, the ROS message definition matters here. This transformation should be in the subscriber callback if wanted.

ljaniec ( 2022-12-19 15:31:11 -0500 )edit

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Asked: 2022-12-15 05:30:58 -0500

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Last updated: Dec 18 '22

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