Converting a string of packed bytes into an array of floats in Javascript

Question

Context

I know that in python you can create an a string representing the packed bytes of an array doing something like such:

import numpy as np

np.array([1, 2], dtype=np.int32).tobytes() 
# returns '\x01\x00\x00\x00\x02\x00\x00\x00'

np.array([1, 2], dtype=np.float32).tobytes() 
# returns '\x00\x00\x80?\x00\x00\x00@'

And they can be decoded using np.fromstring

Question

Currently, my Javascript is receiving a string of packed bytes that encodes an array of floats (i.e. '\x00\x00\x80?\x00\x00\x00@') and I need to decode the array -- what is the best way to do this?

(if it were an array of ints I imagine I could use text-encoding to pull the bytes and then just multiply and add appropriately...)

Thanks,

So I suppose we could manually do the conversion -- apparently that's how protobufs do it... (or maybe we could hijack their method...) — Tomas Reimers
– Tomas Reimers, Commented Jan 27, 2017 at 21:48

georg · Accepted Answer · 2017-01-27 21:54:35Z

5

First, you have to convert a string into a buffer, and then create a Float32Array on that buffer. Optionally, spread it to create a normal Array:

str = '\x00\x00\x80?\x00\x00\x00@'

bytes = Uint8Array.from(str, c => c.charCodeAt(0))
floats = new Float32Array(bytes.buffer)

console.log(floats)

console.log([...floats]);

answered Jan 27, 2017 at 21:54

georg

216k57 gold badges324 silver badges401 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Tomas Reimers Over a year ago

Haha, seems we had just resolved it in the comment above! But appreciate you confirming :)

Community · Accepted Answer · 2017-05-23 12:33:29Z

2

Floating-point representation can vary from platform to platform. It isn't a good idea to use a binary serialized form of a floating-point number to convey a number from one machine to another.

That said, the answers to this question might help you, provided the encoding used by the JavaScript matches that of the source of the numbers:

Read/Write bytes of float in JS

edited May 23, 2017 at 12:33

CommunityBot

11 silver badge

answered Jan 27, 2017 at 21:48

Jonathan Gilbert

3,91026 silver badges32 bronze badges

1 Comment

Tomas Reimers Over a year ago

Interesting, that post gave me a good idea... we could read the string into a uint8 buffer and then use a Float32Array view on the buffer....

Collectives™ on Stack Overflow

Converting a string of packed bytes into an array of floats in Javascript

Context

Question

2 Answers 2

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

Context

Question

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related