Set chunks

Thinking about chunking is important when it comes to analyzing your data, because in most situations this will not fit into memory, hence having the fastest read access to it is crucial for your workflows. For example, for geo-spatial data do you want fast access on time or space, or... think about it.

To determine the chunk size of the array representation on disk, call the setchunks function prior to saving.

Chunking YAXArrays

using YAXArrays, Zarr
a = YAXArray(rand(10,20))
a_chunked = setchunks(a, (5,10))
a_chunked.chunks

2×2 DiskArrays.GridChunks{2, Tuple{DiskArrays.RegularChunks, DiskArrays.RegularChunks}}:
 (1:5, 1:10)   (1:5, 11:20)
 (6:10, 1:10)  (6:10, 11:20)

And the saved file is also splitted into Chunks.

f = tempname()
savecube(a_chunked, f, backend=:zarr)
Cube(f).chunks

2×2 DiskArrays.GridChunks{2, Tuple{DiskArrays.RegularChunks, DiskArrays.RegularChunks}}:
 (1:5, 1:10)   (1:5, 11:20)
 (6:10, 1:10)  (6:10, 11:20)

Alternatively chunk sizes can be given by dimension name, so the following results in the same chunks:

a_chunked = setchunks(a, (Dim_2=10, Dim_1=5))
a_chunked.chunks

2×2 DiskArrays.GridChunks{2, Tuple{DiskArrays.RegularChunks, DiskArrays.RegularChunks}}:
 (1:5, 1:10)   (1:5, 11:20)
 (6:10, 1:10)  (6:10, 11:20)

Chunking Datasets

Setchunks can also be applied to a Dataset.

Set Chunks by Axis

Set chunk size for each axis occuring in a Dataset. This will be applied to all variables in the dataset:

using YAXArrays, Zarr
ds = Dataset(x = YAXArray(rand(10,20)), y = YAXArray(rand(10)), z = YAXArray(rand(10,20,5)))
dschunked = setchunks(ds, Dict("Dim_1"=>5, "Dim_2"=>10, "Dim_3"=>2))
Cube(dschunked).chunks

2×2×3 DiskArrays.GridChunks{3, Tuple{DiskArrays.RegularChunks, DiskArrays.RegularChunks, DiskArrays.RegularChunks}}:
[:, :, 1] =
 (1:5, 1:10, 1:2)   (1:5, 11:20, 1:2)
 (6:10, 1:10, 1:2)  (6:10, 11:20, 1:2)

[:, :, 2] =
 (1:5, 1:10, 3:4)   (1:5, 11:20, 3:4)
 (6:10, 1:10, 3:4)  (6:10, 11:20, 3:4)

[:, :, 3] =
 (1:5, 1:10, 5:5)   (1:5, 11:20, 5:5)
 (6:10, 1:10, 5:5)  (6:10, 11:20, 5:5)

Saving...

f = tempname()
savedataset(dschunked, path=f, driver=:zarr)

YAXArray Dataset
Shared Axes: 
↓ Dim_1 Sampled{Int64} Base.OneTo(10) ForwardOrdered Regular Points
Variables: 

x
  ↓ Dim_2 Sampled{Int64} Base.OneTo(20) ForwardOrdered Regular Pointsy, 
z
  ↓ Dim_2 Sampled{Int64} Base.OneTo(20) ForwardOrdered Regular Points,
  → Dim_3 Sampled{Int64} Base.OneTo(5) ForwardOrdered Regular Points

Set chunking by Variable

The following will set the chunk size for each Variable separately and results in exactly the same chunking as the example above

using YAXArrays, Zarr
ds = Dataset(x = YAXArray(rand(10,20)), y = YAXArray(rand(10)), z = YAXArray(rand(10,20,5)))
dschunked = setchunks(ds,(x = (5,10), y = Dict("Dim_1"=>5), z = (Dim_1 = 5, Dim_2 = 10, Dim_3 = 2)))
Cube(dschunked).chunks

2×2×3 DiskArrays.GridChunks{3, Tuple{DiskArrays.RegularChunks, DiskArrays.RegularChunks, DiskArrays.RegularChunks}}:
[:, :, 1] =
 (1:5, 1:10, 1:2)   (1:5, 11:20, 1:2)
 (6:10, 1:10, 1:2)  (6:10, 11:20, 1:2)

[:, :, 2] =
 (1:5, 1:10, 3:4)   (1:5, 11:20, 3:4)
 (6:10, 1:10, 3:4)  (6:10, 11:20, 3:4)

[:, :, 3] =
 (1:5, 1:10, 5:5)   (1:5, 11:20, 5:5)
 (6:10, 1:10, 5:5)  (6:10, 11:20, 5:5)

saving...

f = tempname()
savedataset(dschunked, path=f, driver=:zarr)

YAXArray Dataset
Shared Axes: 
↓ Dim_1 Sampled{Int64} Base.OneTo(10) ForwardOrdered Regular Points
Variables: 

x
  ↓ Dim_2 Sampled{Int64} Base.OneTo(20) ForwardOrdered Regular Pointsy, 
z
  ↓ Dim_2 Sampled{Int64} Base.OneTo(20) ForwardOrdered Regular Points,
  → Dim_3 Sampled{Int64} Base.OneTo(5) ForwardOrdered Regular Points

Set chunking for all variables

The following code snippet only works when all member variables of the dataset have the same shape and sets the output chunks for all arrays.

using YAXArrays, Zarr
ds = Dataset(x = YAXArray(rand(10,20)), y = YAXArray(rand(10,20)), z = YAXArray(rand(10,20)))
dschunked = setchunks(ds,(5,10))
Cube(dschunked).chunks

2×2×3 DiskArrays.GridChunks{3, Tuple{DiskArrays.RegularChunks, DiskArrays.RegularChunks, DiskArrays.RegularChunks}}:
[:, :, 1] =
 (1:5, 1:10, 1:1)   (1:5, 11:20, 1:1)
 (6:10, 1:10, 1:1)  (6:10, 11:20, 1:1)

[:, :, 2] =
 (1:5, 1:10, 2:2)   (1:5, 11:20, 2:2)
 (6:10, 1:10, 2:2)  (6:10, 11:20, 2:2)

[:, :, 3] =
 (1:5, 1:10, 3:3)   (1:5, 11:20, 3:3)
 (6:10, 1:10, 3:3)  (6:10, 11:20, 3:3)

saving...

f = tempname()
savedataset(dschunked, path=f, driver=:zarr)

YAXArray Dataset
Shared Axes: 
↓ Dim_1 Sampled{Int64} Base.OneTo(10) ForwardOrdered Regular Points,
→ Dim_2 Sampled{Int64} Base.OneTo(20) ForwardOrdered Regular Points
Variables: 
x, y, z,

Suggestions on how to improve or add to these examples is welcome.