# Saving data tables at different timepoints

**URL:** <https://discourse.julialang.org/t/saving-data-tables-at-different-timepoints/89267>\
**Category:** Data\
**Tags:** question, dataframes\
**Created:** [October 26, 2022, 4:18am UTC](https://discourse.julialang.org/t/saving-data-tables-at-different-timepoints/89267 "2022-10-26T04:18:03Z")\
**Posts on this page:** 1\
**Showing post:** 5

<div class="post-metadata">

**Author:** ![rocco\_sprmnt21](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rocco_sprmnt21/32/20127_2.png) [@rocco\_sprmnt21](https://discourse.julialang.org/u/rocco_sprmnt21)\
**Post date:** [November 3, 2022, 11:27pm UTC](https://discourse.julialang.org/t/saving-data-tables-at-different-timepoints/89267/5 "2022-11-03T23:27:36Z")

</div>

```julia

df = DataFrame(A=[1,2,3], B=[:x,:y,:z], C=[(1,3), (-2,1),(4,4)])
dfh=DataFrame(s=0,id=0,a=missings(NamedTuple,1),r=missings(NamedTuple,1), m=missings(NamedTuple,1))

push!(dfh,(s=1,id=1,a=copy(df[1,:]),r=missing, m=missing))
push!(dfh,(s=2,id=2,a=copy(df[2,:]),r=missing, m=missing))
push!(dfh,(s=3,id=3,a=copy(df[3,:]),r=missing, m=missing))

#modify
function mh(dfh,row,nt)
    step=maximum(dfh.s)+1
    push!(dfh,(s=step,id=row,a=merge(only(dfh[dfh.id.==row,:a]),nt),r=missing, m=only(dfh[dfh.id.==row,:a])))
end

mh(dfh,2,(B=:Y,))

#remove

function rh(dfh,row)
    step=maximum(dfh.s)+1
    push!(dfh,(s=step,id=row,a=missing,r=only(dfh[dfh.id.==row,:a]), m=missing))
end

rh(dfh,1)

#add
function ah(dfh,nt)
    step=maximum(dfh.s)+1
    mid=maximum(dfh.id)+1
    push!(dfh,(s=step,id=mid,a=nt,r=missing, m=missing))
end

ah(dfh,(A=4,B=:w,C=(9,9)))

#-----
step(n)=combine(groupby(dfh[1:n+1,:],:id),:a=>x->[last(x)])

julia> step(6)
5×2 DataFrame
 Row │ id a_function
     │ Int64 NamedTupl…?
─────┼─────────────────────────────────────
   1 │ 0 missing
   2 │ 1 missing
   3 │ 2 (A = 2, B = :Y, C = (-2, 1))
   4 │ 3 (A = 3, B = :z, C = (4, 4))
   5 │ 4 (A = 4, B = :w, C = (9, 9))

julia> step(4)
4×2 DataFrame
 Row │ id a_function
     │ Int64 NamedTupl…?
─────┼─────────────────────────────────────
   1 │ 0 missing
   2 │ 1 (A = 1, B = :x, C = (1, 3))
   3 │ 2 (A = 2, B = :Y, C = (-2, 1))
   4 │ 3 (A = 3, B = :z, C = (4, 4))

```

PS  
I ask for clarification on the following error obtained in the first attempt to define the `step()` function

```julia
julia> dfh
7×5 DataFrame
 Row │ s id a r ⋯
     │ Int64 Int64 NamedTup…? NamedTup…? ⋯
─────┼───────────────────────────────────────────────────────────────────────────
   1 │ 0 0 missing missing ⋯
   2 │ 1 1 (A = 1, B = :x, C = (1, 3)) missing
   3 │ 2 2 (A = 2, B = :y, C = (-2, 1)) missing
   4 │ 3 3 (A = 3, B = :z, C = (4, 4)) missing
   5 │ 4 2 (A = 2, B = :Y, C = (-2, 1)) missing ⋯
   6 │ 5 1 missing (A = 1, B = :x, C = (1, 3))   
   7 │ 6 4 (A = 4, B = :w, C = (9, 9)) missing
                                                                 1 column omitted

julia> combine(groupby(dfh,:id),:a=>last)
ERROR: ArgumentError: function must return only single-column values, or only multiple-column values

```

---

_[View the full topic](https://discourse.julialang.org/t/saving-data-tables-at-different-timepoints/89267)._