What does the `--` value mean in a numpy array?

Question

I found that in some other people's data, the value "--" sometimes appear in an numpy array. How to set an array element to be "--" ?

something like this:

[-- -- -- -- -- -- -- -- 0.27969929575920105 0.27994874119758606
 0.27715885639190674 0.26716524362564087 0.2594984173774719
 0.2584466338157654 0.2565436065196991 0.2539260685443878
 0.2531115710735321 0.25570642948150635 0.2644173204898834
 0.26860886812210083]

Answer 1

That's a NumPy " masked array ." It carries with it an array of booleans, and where they are True the data is understood to be invalid--and hence printed as -- .

If you want to see the masked data, it's accessible using the .data property of the masked array (which of course you can print).