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Add view kwarg to first and last #2951

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Dec 1, 2021
Merged

Add view kwarg to first and last #2951

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b7968ad
Add `view` kwarg to `first` and `last`
Chandu-4444 Nov 30, 2021
22c13ae
Improve tests and formatted `first` `last`
Chandu-4444 Nov 30, 2021
e94cd5a
Refactor `first` `last` a bit
Chandu-4444 Nov 30, 2021
a47176f
Fix tests
Chandu-4444 Nov 30, 2021
63dc6a4
Apply suggestions from code review
bkamins Nov 30, 2021
69868d5
Update test/dataframe.jl
bkamins Nov 30, 2021
7ab4f94
Update NEWS.md
bkamins Nov 30, 2021
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18 changes: 14 additions & 4 deletions src/abstractdataframe/abstractdataframe.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -486,11 +486,16 @@ Get the first row of `df` as a `DataFrameRow`.
Base.first(df::AbstractDataFrame) = df[1, :]

"""
first(df::AbstractDataFrame, n::Integer)
first(df::AbstractDataFrame, n::Integer, view::Bool=false)

Get a data frame with the `n` first rows of `df`.

If `view=false` a freshly allocated `DataFrame` is returned.
If `view=true` then a `SubDataFrame` view into `df` is returned.
"""
Base.first(df::AbstractDataFrame, n::Integer) = df[1:min(n, nrow(df)), :]
function Base.first(df::AbstractDataFrame, n::Integer, view::Bool=false)
return view ? Base.view(df, 1:min(n ,nrow(df)), :) : df[1:min(n, nrow(df)), :]
end

"""
last(df::AbstractDataFrame)
Expand All @@ -500,11 +505,16 @@ Get the last row of `df` as a `DataFrameRow`.
Base.last(df::AbstractDataFrame) = df[nrow(df), :]

"""
last(df::AbstractDataFrame, n::Integer)
last(df::AbstractDataFrame, n::Integer, view::Bool=false)

Get a data frame with the `n` last rows of `df`.

If `view=false` a freshly allocated `DataFrame` is returned.
If `view=true` then a `SubDataFrame` view into `df` is returned.
"""
Base.last(df::AbstractDataFrame, n::Integer) = df[max(1, nrow(df)-n+1):nrow(df), :]
function Base.last(df::AbstractDataFrame, n::Integer, view::Bool=false)
return view ? Base.view(df, max(1, nrow(df)-n+1):nrow(df), :) : df[max(1, nrow(df)-n+1):nrow(df), :]
end


"""
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5 changes: 5 additions & 0 deletions test/dataframe.jl
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Expand Up @@ -1105,6 +1105,11 @@ end
@test last(df, 6) == DataFrame(A=5:10)
@test last(df, 1) == DataFrame(A=10)

@test first(df, 6, true) isa SubDataFrame
@test first(df, 6, false) isa DataFrame
@test last(df, 6, true) isa SubDataFrame
@test last(df, 6, false) isa DataFrame

@test_throws ArgumentError only(df)
@test_throws ArgumentError only(DataFrame())
df = DataFrame(a=1, b=2)
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