protocol buffers - store an double array, 1D, 2D and 3D

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How can be an array of double (1D) stored using protocol buffer? What about multi-dimensional (2D or 3D) dense arrays?

multidimensional-array protocol-buffers c++
3 Answers

If your main goal is a denser JSON representation, you could use the "well known type" [google.protobuf.ListValue][1] for the second dimension:

import "google/protobuf/struct.proto";
message DoubleMatrix {
  uint32 cols = 1;
  uint32 rows = 2;
  repeated google.protobuf.ListValue values = 3;
}

This will produce an array of arrays when marshaling the data to JSON.

{
  "cols": 2,
  "rows": 2,
  "values": [[1, 2], [3, 4]]
}

The downside is that the ListValue type internally uses an inner type that uses the one-of pattern for the values. This may be more cumbersome to handle in your source code than using your own inner type without all the magic.

[1] https://developers.google.com/protocol-buffers/docs/reference/google.protobuf#google.protobuf.ListValue

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