Review changes.

src/Impute.jl

@@ -28,7 +28,7 @@ function __init__()
 
     @warn(
         """
-        All matrix imputation methods will be switching to the JuliaStats column-major convention
+        All matrix imputation methods will be switching to the column-major convention
         (e.g., each column corresponds to an observation, and each row corresponds to a variable).
         """
     )
@@ -51,31 +51,27 @@ Base.showerror(io::IO, err::ImputeError) = println(io, "ImputeError: $(err.msg)"
 include("context.jl")
 include("imputors.jl")
 
-const global imputation_methods = Dict{Symbol, Type}(
-    :drop => DropObs,
-    :dropobs => DropObs,
-    :dropvars => DropVars,
-    :interp => Interpolate,
-    :fill => Fill,
-    :locf => LOCF,
-    :nocb => NOCB,
+const global imputation_methods = (
+    drop = DropObs,
+    dropobs = DropObs,
+    dropvars = DropVars,
+    interp = Interpolate,
+    fill = Fill,
+    locf = LOCF,
+    nocb = NOCB,
 )
 
 include("deprecated.jl")
 
-let
-    for (k, v) in imputation_methods
-        local typename = nameof(v)
-        local f = k
-        local f! = Symbol(k, :!)
-
-        # NOTE: The
-        @eval begin
-            $f(data; kwargs...) = impute($typename(; _extract_context_kwargs(kwargs...)...), data)
-            $f!(data; kwargs...) = impute!($typename(; _extract_context_kwargs(kwargs...)...), data)
-            $f(; kwargs...) = data -> impute($typename(; _extract_context_kwargs(kwargs...)...), data)
-            $f!(; kwargs...) = data -> impute!($typename(; _extract_context_kwargs(kwargs...)...), data)
-        end
+for (f, v) in pairs(imputation_methods)
+    typename = nameof(v)
+    f! = Symbol(f, :!)
+
+    @eval begin
+        $f(data; kwargs...) = impute($typename(; _extract_context_kwargs(kwargs...)...), data)
+        $f!(data; kwargs...) = impute!($typename(; _extract_context_kwargs(kwargs...)...), data)
+        $f(; kwargs...) = data -> impute($typename(; _extract_context_kwargs(kwargs...)...), data)
+        $f!(; kwargs...) = data -> impute!($typename(; _extract_context_kwargs(kwargs...)...), data)
     end
 end
 

src/context.jl

@@ -5,6 +5,10 @@ An imputation context records summary information about missing data for an impu
 """
 abstract type AbstractContext end
 
+# We implement a version of copy for all contexts which reconstructs the context from the
+# raw fields.
+Base.copy(ctx::T) where {T <: AbstractContext} = T(fieldvalues(ctx)...)
+
 """
     ismissing(ctx::AbstractContext, x) -> Bool
 
@@ -18,23 +22,23 @@ exceeds our `ctx.limit` we throw an `ImputeError`
 * `x`: the value to check (may be an single values, abstract array or row)
 """
 function Base.ismissing(ctx::AbstractContext, x)
-    missing = if isa(x, NamedTuple)
-        any(entry -> ctx.is_missing(entry[2]), pairs(x))
+    was_missing = if isa(x, NamedTuple)
+        any(ctx.is_missing, Tuple(x))
     elseif isa(x, AbstractArray)
         any(ctx.is_missing, x)
     else
         ctx.is_missing(x)
     end
 
-    missing_update!(ctx, missing)
+    missing_update!(ctx, was_missing)
 
-    return missing
+    return was_missing
 end
 
 """
     findfirst(ctx::AbstractContext, data::AbstractVector) -> Int
 
-Returns the first not missing index in `data`.
+Returns the first non-missing index in `data`.
 
 # Arguments
 * `ctx::AbstractContext`: the context to pass into `ismissing`
@@ -50,7 +54,7 @@ end
 """
     findlast(ctx::AbstractContext, data::AbstractVector) -> Int
 
-Returns the last not missing index in `data`.
+Returns the last non-missing index in `data`.
 
 # Arguments
 * `ctx::AbstractContext`: the context to pass into `ismissing`
@@ -66,7 +70,7 @@ end
 """
     findnext(ctx::AbstractContext, data::AbstractVector) -> Int
 
-Returns the next not missing index in `data`.
+Returns the next non-missing index in `data`.
 
 # Arguments
 * `ctx::AbstractContext`: the context to pass into `ismissing`
@@ -88,7 +92,7 @@ weighted.
 # Fields
 * `n::Int`: number of observations
 * `count::Int`: number of missing values found
-* `limit::Float64`: allowable limit for missing values to impute
+* `limit::Float64`: allowable portion of total values allowed to be imputed (should be between 0.0 and 1.0).
 * `is_missing::Function`: returns a Bool if the value counts as missing
 * `on_complete::Function`: a function to run when imputation is complete
 """
@@ -105,37 +109,35 @@ function Context(;
     is_missing::Function=ismissing,
     on_complete::Function=complete
 )
-    Context(0, 0, limit, is_missing, on_complete)
+    return Context(0, 0, limit, is_missing, on_complete)
 end
 
-function (ctx::Context)(f::Function)
+function Base.empty(ctx::Context)
     _ctx = copy(ctx)
     _ctx.num = 0
     _ctx.count = 0
 
-    result = f(_ctx)
-    ctx.on_complete(_ctx)
-    return result
+    return _ctx
 end
 
-Base.copy(x::Context) = Context(x.num, x.count, x.limit, x.is_missing, x.on_complete)
-
-function missing_update!(ctx::Context, miss)
+function missing_update!(ctx::Context, was_missing)
     ctx.num += 1
 
-    if miss
+    if was_missing
         ctx.count += 1
     end
 end
 
-function complete(ctx::Context)
+function complete(ctx::Context, data)
     missing_ratio = ctx.count / ctx.num
 
     if missing_ratio > ctx.limit
         throw(ImputeError(
             "More than $(ctx.limit * 100)% of values were missing ($missing_ratio)."
         ))
     end
+
+    return data
 end
 
 
@@ -149,11 +151,11 @@ This context type can be useful if some missing observation are more important t
 # Fields
 * `num::Int`: number of observations
 * `s::Float64`: sum of missing values weights
-* `limit::Float64`: allowable limit for missing values to impute
+* `limit::Float64`: allowable portion of total values allowed to be imputed (should be between 0.0 and 1.0).
 * `is_missing::Function`: returns a Bool if the value counts as missing
-* `on_complete::Function`: a function to run when imputation is complete
+* `on_complete::Function`: allowable portion of total values allowed to be imputed (should be between 0.0 and 1.0).
 * `wv::AbstractWeights`: a set of statistical weights to use when evaluating the importance
-  of each observation
+  of each observation. Will be accumulated during imputation.
 """
 mutable struct WeightedContext <: AbstractContext
     num::Int
@@ -170,37 +172,42 @@ function WeightedContext(
     is_missing::Function=ismissing,
     on_complete::Function=complete
 )
-    WeightedContext(0, 0.0, limit, is_missing, on_complete, wv)
+    return WeightedContext(0, 0.0, limit, is_missing, on_complete, wv)
 end
 
-function (ctx::WeightedContext)(f::Function)
+function Base.empty(ctx::WeightedContext)
     _ctx = copy(ctx)
     _ctx.num = 0
     _ctx.s = 0.0
 
-    result = f(_ctx)
-    ctx.on_complete(_ctx)
-    return result
-end
-
-function Base.copy(x::WeightedContext)
-    WeightedContext(x.num, x.s, x.limit, x.is_missing, x.on_complete, x.wv)
+    return _ctx
 end
 
-function missing_update!(ctx::WeightedContext, miss)
+function missing_update!(ctx::WeightedContext, was_missing)
     ctx.num += 1
 
-    if miss
+    if was_missing
         ctx.s += ctx.wv[ctx.num]
     end
 end
 
-function complete(ctx::WeightedContext)
+function complete(ctx::WeightedContext, data)
     missing_ratio = ctx.s / sum(ctx.wv)
 
     if missing_ratio > ctx.limit
         throw(ImputeError(
             "More than $(ctx.limit * 100)% of weighted values were missing ($missing_ratio)."
         ))
     end
+
+    return data
+end
+
+for T in [Context, WeightedContext]
+    @eval begin
+        function (ctx::$T)(f::Function)
+            _ctx = empty(ctx)
+            return ctx.on_complete(_ctx, f(_ctx))
+        end
+    end
 end

src/deprecated.jl

@@ -10,6 +10,7 @@ Base.@deprecate(
     impute!(imp::Imputor, context::AbstractContext, data; kwargs...),
     impute!(typeof(imp)(; context=context), data; kwargs...)
 )
+
 #####################################################################
 # Deprecate all impute calls where the first argument is an Imputor #
 #####################################################################
@@ -88,6 +89,7 @@ function impute(data, args...; kwargs...)
         """,
         :impute
     )
+    # Call `deepcopy` because we can trust that it's available for all types.
     return impute!(deepcopy(data), args...; kwargs...)
 end
 
@@ -148,8 +150,8 @@ function chain(data, args...; kwargs...)
         """,
         :chain
     )
-    result = deepcopy(data)
-    return chain!(data, args...; kwargs...)
+    # Call `deepcopy` because we can trust that it's available for all types.
+    return chain!(deepcopy(data), args...; kwargs...)
 end
 
 #####################

src/imputors.jl

@@ -13,10 +13,11 @@ abstract type Imputor end
 """
     impute(imp::Imputor, data)
 
-Copies the `data` before calling the corresponding `impute!(imp, ...)` call.
+Returns a new copy of the `data` with the missing data imputed by the imputor `imp`.
 """
 function impute(imp::Imputor, data)
-    impute!(imp, deepcopy(data))
+    # Call `deepcopy` because we can trust that it's available for all types.
+    return impute!(imp, deepcopy(data))
 end
 
 """
@@ -33,7 +34,7 @@ if this is not the desired behaviour custom imputor methods should overload this
 * `AbstractMatrix`: the input `data` with values imputed
 """
 function impute!(imp::Imputor, data::AbstractMatrix)
-    for i in 1:size(data, 2)
+    for i in axes(data, 2)
         impute!(imp, view(data, :, i))
     end
     return data

src/imputors/drop.jl

@@ -11,7 +11,6 @@ struct DropObs <: Imputor
     context::AbstractContext
 end
 
-"""DropObs(; context=Context()) -> DropObs"""
 DropObs(; context=Context()) = DropObs(context)
 
 """
@@ -54,7 +53,9 @@ NOTES (or premature optimizations):
 """
 function impute!(imp::DropObs, data::AbstractMatrix)
     imp.context() do c
-        mask = map(i -> !ismissing(c, data[i, :]), 1:size(data, 1))
+        mask = map(axes(data, 1)) do i
+            !ismissing(c, view(data, i, :))
+        end
         return data[mask, :]
     end
 end
@@ -101,7 +102,6 @@ struct DropVars <: Imputor
     context::AbstractContext
 end
 
-"""DropVars(; context=Context()) -> DropVars"""
 DropVars(; context=Context()) = DropVars(context)
 
 """
@@ -119,10 +119,10 @@ requires copying the matrix.
 * `AbstractMatrix`: a new matrix with missing columns removed
 """
 function impute!(imp::DropVars, data::AbstractMatrix)
-    mask = map(1:size(data, 2)) do i
+    mask = map(axes(data, 2)) do i
         try
             imp.context() do c
-                for j in 1:size(data, 1)
+                for j in axes(data, 1)
                     ismissing(c, data[j, i])
                 end
             end

src/imputors/fill.jl

@@ -20,13 +20,15 @@ Fill(; value=mean, context=Context()) = Fill(value, context)
 """
     impute!(imp::Fill, data::AbstractVector)
 
-Computes the fill value if `imp.value` is a `Function` (i.e., `imp.value(drop(copy(data)))`)
-and replaces all missing values in the `data` with that value.
+Fill in missing values with a values determined by `imp.value`.
+If `imp.value`  is a function then the fill values calculated by invoking that function on
+the collection of all nonmissing values.
 """
 function impute!(imp::Fill, data::AbstractVector)
     imp.context() do c
         fill_val = if isa(imp.value, Function)
-            imp.value(Iterators.drop(copy(data); context=c))
+            # Call `deepcopy` because we can trust that it's available for all types.
+            imp.value(Iterators.drop(deepcopy(data); context=c))
         else
             imp.value
         end

src/imputors/interp.jl

@@ -23,7 +23,7 @@ function impute!(imp::Interpolate, data::AbstractVector{<:Union{T, Missing}}) wh
     imp.context() do c
         i = findfirst(c, data) + 1
 
-        while i < length(data)
+        while i < lastindex(data)
             if ismissing(c, data[i])
                 prev_idx = i - 1
                 next_idx = findnext(c, data, i + 1)

src/imputors/locf.jl

@@ -1,3 +1,12 @@
+"""
+    LOCF <: Imputor
+
+Last observation carried forward. Fill in missing values with the most recent
+nonmissing value.
+
+See also:
+- [NOCB](@ref): Next Observation Carried Backward
+"""
 struct LOCF <: Imputor
     context::AbstractContext
 end
@@ -14,16 +23,11 @@ existing observation.
 WARNING: missing elements at the head of the array may not be imputed if there is no
 existing observation to carry forward. As a result, this method does not guarantee
 that all missing values will be imputed.
-
-# Usage
-```
-
-```
 """
 function impute!(imp::LOCF, data::AbstractVector)
     imp.context() do c
         start_idx = findfirst(c, data) + 1
-        for i in start_idx:length(data)
+        for i in start_idx:lastindex(data)
             if ismissing(c, data[i])
                 data[i] = data[i-1]
             end