PyTorch NDArray operators¶

In the following examples, we assume

manager is an instance of ai.djl.ndarray.NDManager
- it is recommended to look through https://docs.djl.ai/master/docs/development/memory_management.html in advance so that you can get better insight of NDManager
$tensor is a placeholder for an instance of torch.tensor
$ndarray is a placeholder for an instance of ai.djl.ndarray.NDArray
you import the following packages

import ai.djl.ndarray.*; import ai.djl.ndarray.types.*;

Data types¶

torch	djl
`torch.bool`	`DataType.BOOLEAN`
`torch.uint8`	`DataType.UINT8`
`torch.int8`	`DataType.INT8`
`torch.int16`,`torch.short`	`DataType.INT16`
`torch.int32`,`torch.int`	`DataType.INT32`
`torch.int64`,`torch.long`	`DataType.INT64`
`torch.float16`,`torch.half`	`DataType.FLOAT16`
`torch.float32`,`torch.float`	`DataType.FLOAT32`
`torch.float64`,`torch.double`	`DataType.FLOAT64`

NDArray creation¶

torch	djl	note
`tensor.tensor(array)`	`manager.create(array)`	`array` may be `[v0,v1,...]` or `[[v0,v1,...],...]`
`$tensor.to('cpu')`	`$ndarray.toDevice(Device.cpu(),false)`
`torch.zeros(p,q,r)`	`manager.zeros(new Shape(p,q,r))`
`torch.ones(p,q,r)`	`manager.ones(new Shape(p,q,r))`
`torch.zeros_like($tensor)`	`$ndarray.zerosLike()`, `manager.zeros($ndarray.getShape())`
`torch.ones_like($tensor)`	`$ndarray.onesLike()`, `manager.ones($ndarray.getShape())`
`torch.full((p,q),fill_value=s)`	`manager.full(new Shape(p,q),r)`
`torch.rand(p,q,r)`	`manager.randomUniform(from,to,new Shape(p,q,r))`	`randomUniform` requires a range
`torch.randn(p,q,r)`	`manager.randomNormal(new Shape(p,q,r))`
`torch.arange(p,q,r)`	`manager.arange(p,q,r)`
`torch.linspace(p,q,r)`	`manager.linspace(p,q,r)`
`torch.eye(n)`	`manager.eye(n)`

create a tensor from array¶

`torch.tensor`/`manager.create`¶

a = [
    [1, 2, 3],
    [4, 5, 6]
]
tensor.tensor(a)

float[][] array = { {1, 2, 3}, {4, 5, 6} };
NDArray nd = manager.create(array);

show output

ND: (2, 3) cpu() float32
[
  [1., 2., 3.],
  [4., 5., 6.],
]

`to('cpu')`/`toDevice(Device.cpu())`¶

NDArray nd = manager.create(new float[] {1, 2, 3, 4, 5});
nd = nd.toDevice(Device.cpu(), false);
// OR
nd = nd.toDevice(Device.gpu(), false);

create zero and one tensor¶

ones, zeros, ones_like and zeros_like¶

torch.ones(1, 2, 3)
torch.zeros(1, 2, 3)
a = [
    [1, 2, 3],
    [4, 5, 6]
]
torch.ones_like(a)
torch.zeros_like(a)

NDArray ones = manager.ones(new Shape(1, 2, 3));
NDarray zeros = manager.zeros(new Shape(1, 2, 3));

NDArray a = manager.create(new float[][] { {1, 2, 3}, {4, 5, 6} });
ones = a.onesLike();
zeros= a.zerosLike();

create a tensor from array with gradient¶

NDArray doesn't hold gradient by default and you have to explicitly require grad.

a = [
    [1, 2, 3],
    [4, 5, 6]
]
torch.tensor(a, requires_grad=True, dtype=float)

NDArray a = manager.create(new float[][] { {1, 2, 3}, {4, 5, 6} });
a.setRequiresGradient(true);
a

show output

ND: (2, 3) cpu() float32 hasGradient
[
  [1., 2., 3.],
  [4., 5., 6.],
]

create a tensor filled with values¶

Python

# fill by value
torch.full((2, 3), fill_value=42)
# fill by random value
torch.rand(1, 2, 3)  # [0,1) uniform distribution
torch.randn(1, 2, 3)  # (0,1) normal distribution
torch.randint(0, 5, (1, 2, 3))

# fill by sequential values
torch.arange(1, 5, 0.5)
torch.linspace(1, 4, 5)

# diag
torch.eye(3)

full¶

manager.full(new Shape(2, 3), 42);

show output

ND: (2, 3) cpu() int32
[
 [42, 42, 42],
 [42, 42, 42],
]

rand/randomUniform¶

Different from Python, you need to specify a range of uniform distribution.

var from = 0;
var to = 1;
manager.randomUniform(from, to, new Shape(1, 2, 3));

show output

ND: (1, 2, 3) cpu() float32
[
  [
    [0.1044, 0.1518, 0.8869],
    [0.8307, 0.4503, 0.0178],
  ],
]

random/randomNormal¶

manager.randomNormal(new Shape(1, 2, 3));

show output

ND: (1, 2, 3) cpu() float32
[
  [
    [-1.7142,  0.8033, -0.406 ],
    [-1.8686, -0.3713,  0.4713],
  ],
]

arange and linspace¶

manager.arange(1f, 4f, 0.5f);

show output

ND: (6) cpu() float32
[1. , 1.5, 2. , 2.5, 3. , 3.5]

manager.linspace(1f,4f,5);

show output

ND: (5) cpu() float32
[1.  , 1.75, 2.5 , 3.25, 4.  ]

eye¶

manager.eye(3);

show output

ND: (3, 3) cpu() float32
[
  [1., 0., 0.],
  [0., 1., 0.],
  [0., 0., 1.],
]

size, shape and transform¶

overview¶

torch	djl	note
`tensor.size()`	`$ndarray.getShape()`	2x3x4 tensor/ndarray returns `(2,3,4)`
`tensor.ndim()`	`$ndarray.getShape().dimension()`	2x3x4 tensor returns `3`
???	`$ndarray.size()`	2x3x4 ndarray returns `24`
`tensor.reshape(p,q)`	`$ndarray.reshape(p,q)`
`torch.flatten($tensor)`	`$ndarray.flatten()`
`torch.squeeze($tensor)`	`$ndarray.squeeze()`
`torch.unsqueeze(tensor,dim)`	`$ndarray.expandDims(dim)`
`tensor.T, torch.t($tensor)`	`$ndarray.transpose()`
`torch.transpose(tensor,d0,d1)`	`$ndarray.transpose(d0,d1)`

Size and Shape¶

get size and shape¶

var a = manager.zeros(new Shape(2, 3, 4))

a.getShape().dimension(); // => 3
a.getShape(); // => (2, 3, 4)
a.size(); // => 24

reshape¶

var a = manager.zeros(new Shape(2, 3, 4));

show output

ND: (2, 3, 4) cpu() float32
[
  [
    [0., 0., 0., 0.],
    [0., 0., 0., 0.],
    [0., 0., 0., 0.],
  ],
  [
    [0., 0., 0., 0.],
    [0., 0., 0., 0.],
    [0., 0., 0., 0.],
  ],
]

a.reshape(new Shape(6, 4));
// is equal to a.reshape(new Shape(6, -1))

show output

ND: (6, 4) cpu() float32
[
  [0., 0., 0., 0.],
  [0., 0., 0., 0.],
  [0., 0., 0., 0.],
  [0., 0., 0., 0.],
  [0., 0., 0., 0.],
  [0., 0., 0., 0.],
]

flatten¶

a.flatten();
// is equal to a.reshape(-1)

show output

ND: (24) cpu() float32
[0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., ... 4 more]

You can also specify flatten dimension.

a.flatten(1,2);

show output

ND: (2, 12) cpu() float32
[
  [0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
  [0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.],
]

Transform¶

squeeze¶

squeeze Removes all singleton dimensions from this NDArray Shape.

var a = manager.zeros(new Shape(2, 1, 2));

[[0., 0.]] has a redundant dimension. squeeze method drops this dimension.

ND: (2, 1, 2) cpu() float32
[
    [[0., 0.]],
    [[0., 0.]],
]

a.squeeze();

show output

ND: (2, 2) cpu() float32
[
  [0., 0.],
  [0., 0.],
]

You can also drop only specific singleton dimensions.

var a = manager.zeros(2, 1, 2, 1);

ND: (2, 1, 2, 1) cpu() float32
[
  [[[0.],[0.]]],
  [[[0.],[0.]]],
]

a.squeeze(1);

show output

ND: (2, 2, 1) cpu() float32
[
  [[0.],[0.],],
  [[0.],[0.],],
]

unsqueeze/expandDims¶

Python

a = torch.zeros(2, 2)
torch.unsqueeze(a, 0)

Java

var a = manager.zeros(new Shape(2,2));

ND: (2, 2) cpu() float32
[
  [0., 0.],
  [0., 0.],
]

a.expandDims(0);

show output

ND: (1, 2, 2) cpu() float32
[[
    [0., 0.],
    [0., 0.],
]]

var a = manager.create(new int[] {10, 20, 30, 40});

ND: (4) cpu() int32
[10, 20, 30, 40]

a.expandDims(-1);

show output

ND: (4, 1) cpu() int32
[
  [10],
  [20],
  [30],
  [40],
]

Transpose¶

Python

m = [
    [1, 2],
    [3, 4],
]
a = torch.tensor(m)
a.T

Java

var a = manager.create(new float[][] { {1, 2}, {3, 4} });
a.transpose();

show output

ND: (2, 2) cpu() int32
[
  [ 1,  3],
  [ 2,  4],
]

Index and Slice¶

Overview¶

In general, you can replace PyTorch fancy index expression with String interpolation.

torch	djl
`torch.flip(q,(n*))`	`$ndarray.flip(n*)`
`torch.roll(q))`	???
`$tensor[idx]`	`$ndarray.get(idx)`
`$tensor[n:]`	`$ndarray.get("n:")` ,`$ndarray.get("{}:",n)`
`$tensor[[p,q,r]]`	`$ndarray.get(manager.create(new int[] {p,q,r}))`
`$tensor[n,m]`	`$ndarray.get(n,m)`
`$tensor[$indices]`	`$ndarray.get($indices)`	`$indices` is int tensor/ndarray of shape 2 x 2
`$tensor[:,n]`	`$ndarray.get(":,{}",n)`
`$tensor[:,n:m]`	`$ndarray.get(":,{}:{}",n,m)`
`$tensor[:,[n,m]]`	`$ndarray.get(":,{}",$colIndices)`	`$colIndices` is `NDArray {n, m}`.
`$tensor[[p,q,r],[s,t,u]]`	`$ndarray.get("{},{}",$rowIndices,$colIndices)`	`$tensor` and `$ndarray` are 2 dimension tensor/ndarray. `$rowIndices` and `$colIndices` are 1 dimension int ndarray
`$tensor[[[p],[q],[r]],[s,t]]`	`$ndarray.get("{},{}",$rowIndices.expandDims(-1),$colIndices)`	`rowIndices` is `NDArray {p, q, r}`

1 dimension ndarray slice¶

var a = manager.arange(0, 100, 10);

a.get("5:");

show output

ND: (5) cpu() int32
[ 50,  60,  70,  80,  90]

a.get("{}:",5);

show output

ND: (5) cpu() int32
[ 50,  60,  70,  80,  90]

var indices = manager.create(new int[] {1, 3, 2});
a.get(indices);

show output

ND: (3) cpu() int32
[ 10,  30,  20]

var indices = manager.create(new int[][] { {2, 4}, {6, 8} });
a.get(indices);

show output

ND: (2, 2) cpu() int32
[
  [20, 40],
  [60, 80],
]

multi-dimension ndarray slice¶

var a = manager.create(new int[][] { {5, 10, 20}, {30, 40, 50}, {60, 70, 80} });

`$tensor[n,m]`/`$ndarray.get(n,m)`¶

a.get(1, 2);

show output

ND: () cpu() int32
50

`tensor[:,n]` / `ndarray.get(":,{}",n)`¶

var n = 1;
a.get(":,{}", n);

show output

ND: (3) cpu() int32
[10, 40, 70]

`tensor[:,n:m]` / `ndarray.get(":,{}:{}",n,m)`¶

var n = 1;
var m = 2;
a.get(":,{}:{}", n, m);

show output

ND: (3, 1) cpu() int32
[
  [10],
  [40],
  [70],
]

`tensor[:,[n,m]]` / `ndarray.get(":,{}",$colIndices)`¶

var colIndices = manager.create(new int[] {2, 0});
a.get(":,{}", colIndices);

show output

ND: (3, 2) cpu() int32
[
  [20,  0],
  [50, 30],
  [80, 60],
]

`$tensor[[p,q,r],[s,t,u]]` / `$ndarray.get("{},{}",$rowIndices,$colIndices)`¶

var rowIndices = manager.create(new int[] {0, 1, 2});
var colIndices = manager.create(new int[] {2, 0, 1);
// select values at (0,2), (1,0) and (2,1) in 2d ndarray
a.get("{},{}", rowIndices,colIndices);

show output

ND: (3) cpu() int32
[20, 30, 70]

`$tensor[[[p],[q],[r]],[s,t]]`/ `$ndarray.get({},{},$rowIndices.expandDims(-1),$colIndices)`¶

var rowIndices = manager.create(new int[] {0, 1, 2}).expandDims(-1);
var colIndices = manager.create(new int[] {2, 0});
a.get("{},{}", rowIndices,colIndices);

show output

ND: (3, 2) cpu() int32
[
  [20,  0],
  [50, 30],
  [80, 60],
]

flip¶

var a = manager.create(new int[] {1,2,3,4,5,6,7,8}, new Shape(2,2,2));

ND: (2, 2, 2) cpu() int32
[
  [
    [ 1,  2],
    [ 3,  4],
  ],
  [
    [ 5,  6],
    [ 7,  8],
  ],
]

a.flip(0);

show output

[
  [
    [ 5,  6],
    [ 7,  8],
  ],
  [
    [ 1,  2],
    [ 3,  4],
  ],
]

a.flip(1);

show output

[
  [
    [ 3,  4],
    [ 1,  2],
  ],
  [
    [ 7,  8],
    [ 5,  6],
  ],
]

a.flip(2);

show output

ND: (2, 2, 2) cpu() int32
[
  [
    [ 2,  1],
    [ 4,  3],
  ],
  [
    [ 6,  5],
    [ 8,  7],
  ],
]

a.flip(0,1,2);

show output

ND: (2, 2, 2) cpu() int32
[
  [
    [ 8,  7],
    [ 6,  5],
  ],
  [
    [ 4,  3],
    [ 2,  1],
  ],
]

concat and split¶

torch	djl	note
`torch.cat(tensor0,tensor1,n)`	`ndarray0.concat(ndarray1,n)`	vertically concat when `n` is `0` like `np.vstack`, horizontally concat when `n` is `1` like `np.hstack`
`torch.stack($tensor0,$tensor1)`	`$ndarray0.stack($ndarray1)`

concat¶

var zeros = manager.zeros(new Shape(2, 3));
var ones = manager.ones(new Shape(2, 3));

zeros.concat(ones, 0);

show output

ND: (4, 3) cpu() float32
[
  [0., 0., 0.],
  [0., 0., 0.],
  [1., 1., 1.],
  [1., 1., 1.],
]

zeros.concat(ones, 1);

show output

ND: (2, 6) cpu() float32
[
  [0., 0., 0., 1., 1., 1.],
  [0., 0., 0., 1., 1., 1.],
]

stack¶

var images0 = manager.create(new int[][] { {128, 0, 0}, {0, 128, 0} });
var images1 = manager.create(new int[][] { {0, 0, 128}, {127, 127, 127} });

images0.stack(images1);

show output

[
  [
    [128,   0,   0],
    [  0, 128,   0],
  ],
  [
    [  0,   0, 128],
    [127, 127, 127],
  ],
]

images0.stack(images1, 1);

show output

ND: (2, 2, 3) cpu() int32
[
  [
    [128,   0,   0],
    [  0,   0, 128],
  ],
  [
    [  0, 128,   0],
    [127, 127, 127],
  ],
]

images0.stack(images1, 2);

show output

[
  [
    [128,   0],
    [  0,   0],
    [  0, 128],
  ],
  [
    [  0, 127],
    [128, 127],
    [  0, 127],
  ],
]

Arithmetic operations¶

torch	djl
`$tensor + 1`	`$ndarray.add(1)`
`$tensor - 1`	`$ndarray.sub(1)`
`$tensor * 2`	`$ndarray.mul(2)`
`$tensor / 3`	`$ndarray.div(3)`
`torch.mean($tensor)`	`$ndarray.mean()`
`torch.median($tensor)`	`$ndarray.median()`
`torch.sum($tensor)`	`$ndarray.sum()`
`torch.prod($tensor)`	`$ndarray.prod()`
`torch.cumsum($tensor)`	`$ndarray.cumsum()`
`torch.topk($tensor,k,dim)`	`$ndarray.topK(k,dim)`
`torch.kthvalue($tensor,k,dim)`	???
`torch.mode($tensor)`	???
`torch.std($tensor)`	???
`torch.var($tensor)`	???
`torch.std_mean($tensor)`	???
`torch.abs($tensor)`	`$ndarray.abs()`
`torch.ceil($tensor)`	`$ndarray.ceil()`
`torch.round($tensor)`	`$ndarray.round()`
`torch.trunc($tensor)`	`$ndarray.trunc()`
`torch.flac($tensor)`	???
`torch.clamp(tensor,min,max)`	???
`torch.log($tensor)`	`$ndarray.log()`
`torch.log2($tensor)`	`$ndarray.log2()`
`torch.log10($tensor)`	`$ndarray.log10()`
`torch.pow($tensor,n)`	`$ndarray.power(n)`
`torch.pow(n,$tensor)`	???
`torch.sigmoid($tensor)`	`ai.djl.nn.Activation::sigmoid($ndarray)`
`torch.sign($tensor)`	`$ndarray.sign()`
`torch.norm($tensor)`	`$ndarray.norm()`
`torch.dist($tensor0,$tensor,p)`	???
`torch.cdist($tensor0,$tensor,p)`	???

mean¶

torch.mean(tensor)

var a = manager.create(new float[] {0f,1f,2f,3f,4f,5f,6f,7f,8f,9f});
a.mean();

show output

ND: () cpu() float32
4.5

var a = manager.create(new float[] {0f,1f,2f,3f,4f,5f,6f,7f,8f,9f}).reshape(5,2);

a.mean(new int[] {0});
a.mean(new int[] {1});

show output

ND: (2) cpu() float32
[4., 5.]


ND: (5) cpu() float32
[0.5, 2.5, 4.5, 6.5, 8.5]

abs¶

torch.abs(tensor)

var ndarray = manager.create(new int[][] { {1, 2}, {-1, -2} });
ndarray.abs();

show output

ND: (2, 2) cpu() int32
[
  [ 1,  2],
  [ 1,  2],
]

ceil¶

torch.ceil(tensor)

var ndarray = manager.create(new double[][] { {1.0,1.1,1.2,1.3,1.4}, {1.5,1.6,1.7,1.8,1.9} });
ndarray.ceil();

show output

ND: (2, 5) cpu() float64
[
  [1., 2., 2., 2., 2.],
  [2., 2., 2., 2., 2.],
]

floor¶

torch.floor(tensor)

var ndarray = manager.create(new double[][] { {1.0,1.1,1.2,1.3,1.4}, {1.5,1.6,1.7,1.8,1.9} });
ndarray.floor();

show output

ND: (2, 5) cpu() float64
[
  [1., 1., 1., 1., 1.],
  [1., 1., 1., 1., 1.],
]

round¶

torch.round(tensor)

var ndarray = manager.create(new double[][] { {1.0,1.1,1.2,1.3,1.4}, {1.5,1.6,1.7,1.8,1.9} });
ndarray.round();

show output

ND: (2, 5) cpu() float64
[
  [1., 1., 1., 1., 1.],
  [2., 2., 2., 2., 2.],
]

sign¶

torch.sign(tensor)

var ndarray = manager.create(new double[][] { {-0.1, -0.0}, {0.0, 0.1} });
ndarray.sign();

show output

ND: (2, 2) cpu() float64
[
  [-1.,  0.],
  [ 0.,  1.],
]

norm¶

var a = manager.create(new float[] {1f, 1f, 1f});
a.norm();

show output

ND: () cpu() float32
1.7321

checking and filtering¶

torch	djl
`torch.isinf($tensor)`	`$ndarray.isInfinite()`
`torch.isfinite($tensor)`	???
`torch.isnan($tensor)`	`$ndarray.isNaN()`
`torch.nonzero($tensor)`	`$ndarray.nonzero()`
`torch.masked_select(tensor0,maskTensor)`	`$ndarray.booleanMask(maskndarray)`
`torch.where(a, cond)`	???

isinf¶

torch.isinf(tensor)

var ndarray = manager.create(
    new float[][] {
        {Float.NegativeInfinity, Float.MinValue, 0.0f},
        {Float.MaxValue, Float.PositiveInfinity, Float.NaN}
    }
);
ndarray.isInfinite();

show output

[
  [ true, false, false],
  [false,  true, false],
]

isNaN¶

torch.isnan(tensor)

var ndarray = manager.create(
    new float[][] {
        {Float.NegativeInfinity, Float.MinValue, 0.0f},
        {Float.MaxValue, Float.PositiveInfinity, Float.NaN}
    }
);
ndarray.isNaN();

show output

ND: (2, 3) cpu() boolean
[
  [false, false, false],
  [false, false,  true],
]

nonzero¶

a = torch.tensor(
    [
        [0.0, 0.1],
        [0.2, 0.3],
    ])
torch.nonzero()

var a = manager.create(new long[][] { {0.0,0.1}, {0.2,0.3} });
a.nonzero();

show output

ND: (3, 2) cpu() int64
[
  [ 0,  1],
  [ 1,  0],
  [ 1,  1],
]

masked_select/booleanMask¶

t = torch.tensor(
    [
        [0.1, 0.2],
        [0.3, 0.4]
    ]
)
mask = torch.tensor(
    [
        [False, True],
        [True, False]
    ]
)

torch.masked_select(t, mask)

var ndarray = manager.create(new double[][] { {0.1, 0.2}, {0.3, 0.4} });
var mask = manager.create(new boolean[][] { {false, true}, {true,false} });
ndarray.booleanMask(mask);

show output

ND: (2) cpu() float64
[0.2, 0.3]

PyTorch NDArray operators¶

Data types¶

NDArray creation¶

create a tensor from array¶

torch.tensor/manager.create¶

to('cpu')/toDevice(Device.cpu())¶

create zero and one tensor¶

ones, zeros, ones_like and zeros_like¶

create a tensor from array with gradient¶

create a tensor filled with values¶

full¶

rand/randomUniform¶

random/randomNormal¶

arange and linspace¶

eye¶

size, shape and transform¶

overview¶

Size and Shape¶

get size and shape¶

reshape¶

flatten¶

Transform¶

squeeze¶

unsqueeze/expandDims¶

Transpose¶

Index and Slice¶

Overview¶

1 dimension ndarray slice¶

multi-dimension ndarray slice¶

$tensor[n,m]/$ndarray.get(n,m)¶

tensor[:,n] / ndarray.get(":,{}",n)¶

tensor[:,n:m] / ndarray.get(":,{}:{}",n,m)¶

tensor[:,[n,m]] / ndarray.get(":,{}",$colIndices)¶

$tensor[[p,q,r],[s,t,u]] / $ndarray.get("{},{}",$rowIndices,$colIndices)¶

$tensor[[[p],[q],[r]],[s,t]]/ $ndarray.get({},{},$rowIndices.expandDims(-1),$colIndices)¶

flip¶

concat and split¶

concat¶

stack¶

Arithmetic operations¶

mean¶

abs¶

ceil¶

floor¶

round¶

sign¶

norm¶

checking and filtering¶

isinf¶

isNaN¶

nonzero¶

masked_select/booleanMask¶

`torch.tensor`/`manager.create`¶

`to('cpu')`/`toDevice(Device.cpu())`¶

`$tensor[n,m]`/`$ndarray.get(n,m)`¶

`tensor[:,n]` / `ndarray.get(":,{}",n)`¶

`tensor[:,n:m]` / `ndarray.get(":,{}:{}",n,m)`¶

`tensor[:,[n,m]]` / `ndarray.get(":,{}",$colIndices)`¶

`$tensor[[p,q,r],[s,t,u]]` / `$ndarray.get("{},{}",$rowIndices,$colIndices)`¶

`$tensor[[[p],[q],[r]],[s,t]]`/ `$ndarray.get({},{},$rowIndices.expandDims(-1),$colIndices)`¶