Add rowwise function

src/DataFrames.jl

@@ -68,6 +68,7 @@ export AbstractDataFrame,
        head,
        tail,
        permutecols!,
+       rowwise, 
 
        # Remove after deprecation period
        pool,

src/dataframe/dataframe.jl

@@ -1105,4 +1105,4 @@ end
 
 function permutecols!(df::DataFrame, p::AbstractVector{Symbol})
     permutecols!(df, getindex.(index(df).lookup, p))
-end
+end

src/dataframerow/utils.jl

@@ -218,3 +218,28 @@ function Base.getindex(gd::RowGroupDict, dfr::DataFrameRow)
     gix = gd.groups[g_row]
     return view(gd.rperm, gd.starts[gix]:gd.stops[gix])
 end
+
+"""
+    rowwise(f::Function, df::DataFrame)
+
+Performs a function alonw an array from each row in a DataFrame, 
+returning an array of length `nrow(df)`
+
+```julia
+julia> df = DataFrame(a = [2,200], b = [4,400])
+2×2 DataFrames.DataFrame
+│ Row │ a   │ b   │
+├─────┼─────┼─────┤
+│ 1   │ 2   │ 4   │
+│ 2   │ 200 │ 400 │
+
+julia> t = rowwise(mean, df)
+2-element Array{Float64,1}:
+   3.0
+ 300.0
+ ```
+
+"""
+function rowwise(f::Function, df::DataFrame)
+    t = [f([x[2] for x in collect(row)]) for row in eachrow(df)]
+end

src/other/utils.jl

@@ -134,4 +134,4 @@ function _fnames(fs::Vector{T}) where T<:Function
         name
     end
     names
-end
+end

test/dataframerow.jl

@@ -74,6 +74,10 @@ module TestDataFrameRow
     gd = DataFrames.group_rows(df5[1,:])
     @test gd.ngroups == 1
 
+    # rowwise operator 
+    df = DataFrame(a = [2,200], b = [4,400])
+    @test rowwise(Compat.mean, df) = [3.0, 300]
+
     # getproperty, setproperty! and propertynames
     if VERSION >= v"0.7.0-DEV.3067"
         r = DataFrameRow(df, 1)