How to insert a new row in julia at specific index [duplicate] - julia

Question

Is there a way to add a row to an existing dataframe at a specific index?
E.g. you have a dataframe with 3 rows and 1 columns
df = DataFrame(x = [2,3,4])
X
2
3
4
any way to do the following:
insert!(df, 1, [1])
in order to get
X
1
2
3
4
I know that i could probably concat two dataframes df = [df1; df2] but i was hoping to avoid garbaging a large DF whenever i want to insert a row.

Answer 1

In DataFrames 0.21.4 just write (I give two options: one, with broadcasting, is short but creates a temporary object; the other, with foreach is longer to write but allocates a bit less):
julia> df = DataFrame(x = [1,2,3], y = ["a", "b", "c"])
3×2 DataFrame
│ Row │ x │ y │
│ │ Int64 │ String │
├─────┼───────┼────────┤
│ 1 │ 1 │ a │
│ 2 │ 2 │ b │
│ 3 │ 3 │ c │
julia> insert!.(eachcol(df), 2, [4, "d"]) # creates an temporary object but is terse
2-element Array{Array{T,1} where T,1}:
[1, 4, 2, 3]
["a", "d", "b", "c"]
julia> df
4×2 DataFrame
│ Row │ x │ y │
│ │ Int64 │ String │
├─────┼───────┼────────┤
│ 1 │ 1 │ a │
│ 2 │ 4 │ d │
│ 3 │ 2 │ b │
│ 4 │ 3 │ c │
julia> foreach((c, v) -> insert!(c, 2, v), eachcol(df), [4, "d"]) # does not create a temporary object
julia> df
5×2 DataFrame
│ Row │ x │ y │
│ │ Int64 │ String │
├─────┼───────┼────────┤
│ 1 │ 1 │ a │
│ 2 │ 4 │ d │
│ 3 │ 4 │ d │
│ 4 │ 2 │ b │
│ 5 │ 3 │ c │
note that the above operation is not atomic (it may corrupt your data frame if the type of the element you want to add does not match the element type allowed in the column).
If you want a safe operation that will provide automatic promotion use this:
julia> df = DataFrame(x = [1,2,3], y = ["a", "b", "c"])
3×2 DataFrame
│ Row │ x │ y │
│ │ Int64 │ String │
├─────┼───────┼────────┤
│ 1 │ 1 │ a │
│ 2 │ 2 │ b │
│ 3 │ 3 │ c │
julia> [view(df, 1:1, :); DataFrame(names(df) .=> ['a', 'b']); view(df, 3:3, :)]
3×2 DataFrame
│ Row │ x │ y │
│ │ Any │ Any │
├─────┼─────┼─────┤
│ 1 │ 1 │ a │
│ 2 │ 'a' │ 'b' │
│ 3 │ 3 │ c │
(it is a bit slower though and creates a new data frame)
Deprecated
The original answer is here. It was valid for Julia before 1.0 release (and DataFrames.jl version that was compatible with it).
I guess you want to do it in place. Then you can use insert! function like this:
julia> df = DataFrame(x = [1,2,3], y = ["a", "b", "c"])
3×2 DataFrames.DataFrame
│ Row │ x │ y │
├─────┼───┼───┤
│ 1 │ 1 │ a │
│ 2 │ 2 │ b │
│ 3 │ 3 │ c │
julia> foreach((v,n) -> insert!(df[n], 2, v), [4, "d"], names(df))
julia> df
4×2 DataFrames.DataFrame
│ Row │ x │ y │
├─────┼───┼───┤
│ 1 │ 1 │ a │
│ 2 │ 4 │ d │
│ 3 │ 2 │ b │
│ 4 │ 3 │ c │
Of course you have to make sure that you have the right number of columns in the added collection.
If you accept using unexported internal structure of a DataFrame you can do it even simpler:
julia> df = DataFrame(x = [1,2,3], y = ["a", "b", "c"])
3×2 DataFrames.DataFrame
│ Row │ x │ y │
├─────┼───┼───┤
│ 1 │ 1 │ a │
│ 2 │ 2 │ b │
│ 3 │ 3 │ c │
julia> insert!.(df.columns, 2, [4, "d"])
2-element Array{Array{T,1} where T,1}:
[1, 4, 2, 3]
String["a", "d", "b", "c"]
julia> df
4×2 DataFrames.DataFrame
│ Row │ x │ y │
├─────┼───┼───┤
│ 1 │ 1 │ a │
│ 2 │ 4 │ d │
│ 3 │ 2 │ b │
│ 4 │ 3 │ c │