MLUtils
"""
numobs(data)
Return the total number of observations contained in `data`.
If `data` does not have `numobs` defined,
then in the case of `Tables.table(data) == true`
returns the number of rows, otherwise returns `length(data)`.
Authors of custom data containers should implement
`Base.length` for their type instead of `numobs`.
`numobs` should only be implemented for types where there is a
difference between `numobs` and `Base.length`
(such as multi-dimensional arrays).
`getobs` supports by default nested combinations of array, tuple,
named tuples, and dictionaries.
See also [`getobs`](@ref).
# Examples
```jldoctest
# named tuples
x = (a = [1, 2, 3], b = rand(6, 3))
numobs(x) == 3
# dictionaries
x = Dict(:a => [1, 2, 3], :b => rand(6, 3))
numobs(x) == 3
```
All internal containers must have the same number of observations:
```juliarepl
julia> x = (a = [1, 2, 3, 4], b = rand(6, 3));
julia> numobs(x)
ERROR: DimensionMismatch: All data containers must have the same number of observations.
Stacktrace:
[1] _check_numobs_error()
@ MLUtils ~/.julia/dev/MLUtils/src/observation.jl:163
[2] _check_numobs
@ ~/.julia/dev/MLUtils/src/observation.jl:130 [inlined]
[3] numobs(data::NamedTuple{(:a, :b), Tuple{Vector{Int64}, Matrix{Float64}}})
@ MLUtils ~/.julia/dev/MLUtils/src/observation.jl:177
[4] top-level scope
@ REPL[35]:1
```
"""
function
numobs
endGeneric Fallbacks
@
traitfn
numobs
(
data
::
X
)
where
{
X
;
IsTable
{
X
}
}
=
DataAPI
.
nrow
(
data
)
@
traitfn
numobs
(
data
::
X
)
where
{
X
;
!
IsTable
{
X
}
}
=
length
(
data
)
"""
getobs(data, [idx])
Return the observations corresponding to the observation index `idx`.
Note that `idx` can be any type as long as `data` has defined
`getobs` for that type. If `idx` is not provided, then materialize
all observations in `data`.
If `data` does not have `getobs` defined,
then in the case of `Tables.table(data) == true`
returns the row(s) in position `idx`, otherwise returns `data[idx]`.
Authors of custom data containers should implement
`Base.getindex` for their type instead of `getobs`.
`getobs` should only be implemented for types where there is a
difference between `getobs` and `Base.getindex`
(such as multi-dimensional arrays).
The returned observation(s) should be in the form intended to
be passed as-is to some learning algorithm. There is no strict
interface requirement on how this "actual data" must look like.
Every author behind some custom data container can make this
decision themselves.
The output should be consistent when `idx` is a scalar vs vector.
`getobs` supports by default nested combinations of array, tuple,
named tuples, and dictionaries.
See also [`getobs!`](@ref) and [`numobs`](@ref).
# Examples
```jldoctest
# named tuples
x = (a = [1, 2, 3], b = rand(6, 3))
getobs(x, 2) == (a = 2, b = x.b[:, 2])
getobs(x, [1, 3]) == (a = [1, 3], b = x.b[:, [1, 3]])
# dictionaries
x = Dict(:a => [1, 2, 3], :b => rand(6, 3))
getobs(x, 2) == Dict(:a => 2, :b => x[:b][:, 2])
getobs(x, [1, 3]) == Dict(:a => [1, 3], :b => x[:b][:, [1, 3]])
```
"""
function
getobs
endGeneric Fallbacks
getobs
(
data
)
=
data
@
traitfn
getobs
(
data
::
X
,
idx
)
where
{
X
;
IsTable
{
X
}
}
=
Tables
.
subset
(
data
,
idx
,
viewhint
=
false
)
@
traitfn
getobs
(
data
::
X
,
idx
)
where
{
X
;
!
IsTable
{
X
}
}
=
data
[
idx
]
"""
getobs!(buffer, data, idx)
Inplace version of `getobs(data, idx)`. If this method
is defined for the type of `data`, then `buffer` should be used
to store the result, instead of allocating a dedicated object.
Implementing this function is optional. In the case no such
method is provided for the type of `data`, then `buffer` will be
*ignored* and the result of [`getobs`](@ref) returned. This could be
because the type of `data` may not lend itself to the concept
of `copy!`. Thus, supporting a custom `getobs!` is optional
and not required.
See also [`getobs`](@ref) and [`numobs`](@ref).
"""
function
getobs!
endgetobs!(buffer, data) = getobs(data)
getobs!
(
buffer
,
data
,
idx
)
=
getobs
(
data
,
idx
)-------------------------------------------------------------------- AbstractDataContainer Having an AbstractDataContainer allows to define sensible defaults for Base (or other) interfaces based on our interface. This makes it easier for developers by reducing boilerplate.
abstract
type
AbstractDataContainer
end
Base
.
size
(
x
::
AbstractDataContainer
)
=
(
numobs
(
x
)
,
)
Base
.
iterate
(
x
::
AbstractDataContainer
,
state
=
1
)
=
(
state
>
numobs
(
x
)
)
?
nothing
:
(
getobs
(
x
,
state
)
,
state
+
1
)
Base
.
lastindex
(
x
::
AbstractDataContainer
)
=
numobs
(
x
)
Base
.
firstindex
(
::
AbstractDataContainer
)
=
1-------------------------------------------------------------------- Arrays We are very opinionated with arrays: the observation dimension is th last dimension. For different behavior wrap the array in a custom type, e.g. with Tables.table.
numobs
(
A
::
AbstractArray
{
<:
Any
,
N
}
)
where
{
N
}
=
size
(
A
,
N
)0-dim arrays
numobs
(
A
::
AbstractArray
{
<:
Any
,
0
}
)
=
1
function
getobs
(
A
::
AbstractArray
{
<:
Any
,
N
}
,
idx
)
where
N
I
=
ntuple
(
_
->
:
,
N
-
1
)
return
A
[
I
...
,
idx
]
end
getobs
(
A
::
AbstractArray
{
<:
Any
,
0
}
,
idx
)
=
A
[
idx
]
function
getobs!
(
buffer
::
AbstractArray
,
A
::
AbstractArray
{
<:
Any
,
N
}
,
idx
)
where
N
I
=
ntuple
(
_
->
:
,
N
-
1
)
buffer
.=
view
(
A
,
I
...
,
idx
)
return
buffer
end
function
getobs!
(
buffer
::
AbstractArray
,
A
::
AbstractArray
)
buffer
.=
A
return
buffer
end-------------------------------------------------------------------- Tuples and NamedTuples
_check_numobs_error
(
)
=
throw
(
DimensionMismatch
(
"
All data containers must have the same number of observations.
"
)
)
function
_check_numobs
(
data
::
Union
{
Tuple
,
NamedTuple
,
Dict
}
)
length
(
data
)
==
0
&&
return
0
n
=
numobs
(
data
[
first
(
keys
(
data
)
)
]
)
for
i
in
keys
(
data
)
ni
=
numobs
(
data
[
i
]
)
n
==
ni
||
_check_numobs_error
(
)
end
return
n
end
numobs
(
data
::
Union
{
Tuple
,
NamedTuple
}
)
=
_check_numobs
(
data
)
getobs
(
tup
::
Union
{
Tuple
,
NamedTuple
}
)
=
map
(
x
->
getobs
(
x
)
,
tup
)
Base
.
@
propagate_inbounds
function
getobs
(
tup
::
Union
{
Tuple
,
NamedTuple
}
,
indices
)
@
boundscheck
_check_numobs
(
tup
)
return
map
(
x
->
getobs
(
x
,
indices
)
,
tup
)
end
function
getobs!
(
buffers
::
Union
{
Tuple
,
NamedTuple
}
,
tup
::
Union
{
Tuple
,
NamedTuple
}
,
indices
)
_check_numobs
(
tup
)
return
map
(
buffers
,
tup
)
do
buffer
,
x
getobs!
(
buffer
,
x
,
indices
)
end
end
numobs
(
data
::
Dict
)
=
_check_numobs
(
data
)
getobs
(
data
::
Dict
,
i
)
=
Dict
(
k
=>
getobs
(
v
,
i
)
for
(
k
,
v
)
in
pairs
(
data
)
)
getobs
(
data
::
Dict
)
=
Dict
(
k
=>
getobs
(
v
)
for
(
k
,
v
)
in
pairs
(
data
)
)
function
getobs!
(
buffers
,
data
::
Dict
,
i
)
for
(
k
,
v
)
in
pairs
(
data
)
getobs!
(
buffers
[
k
]
,
v
,
i
)
end
return
buffers
end