How to copy a DataFrame structure in an empty DataFrame

[Fred]

Hi,

I have a DataFrame "df" and I would like to create a new DataFrame "m" with  the same colnames than df.  

And then, append to "m" the rows of "df" matching a complex set of conditions, so I need to test many conditions for each row. 

The problem I have is to create an empty dataframe "m" with the sames colnames of "df" and then to append the rows matching conditions to it.

df = readtable("file.tsv")

# trying to create an empty copy of df
m = DataFrame()
names!(m, names(df)) # produce error ArgumentError: Length of nms doesn't match length of x
# but I did not manage to create m with the same cols number than df.


z = size(df)[1]

# for each row of df append the rows matching many conditions on many columns
   for i = 1:z
      if condition(df[:colname_x][i])
        push!(m,i)
      end
  end

Thank you for your comments !

[Milan Bouchet-Valat]

You can use similar() for this:
m = similar(df, 0)


Regards

[Fred]

Thank you very much Milan !
When I searched a solution in DataFrame documentation I did not found the keyword "similar". Is there an equivalent for Julia of this website for Perl for example ?

julia> df = readtable("test2.tsv")
4x4 DataFrames.DataFrame
│ Row │ row1   │ x3_39 │ x2_5 │ x4_5 │
┝━━━━━┿━━━━━━━━┿━━━━━━━┿━━━━━━┿━━━━━━┥
│ 1   │ "row2" │ 3.46  │ 2.7  │ 4.8  │
│ 2   │ "row3" │ 3.58  │ 2.9  │ 4.7  │
│ 3   │ "row4" │ 3.7   │ 2.7  │ 4.9  │
│ 4   │ "row5" │ 3.81  │ 3.0  │ 5.3  │

julia> m = similar(df,0)
0x4 DataFrames.DataFrame


julia> m
0x4 DataFrames.DataFrame

julia> df[2,:]
1x4 DataFrames.DataFrame
│ Row │ row1   │ x3_39 │ x2_5 │ x4_5 │
┝━━━━━┿━━━━━━━━┿━━━━━━━┿━━━━━━┿━━━━━━┥
│ 1   │ "row3" │ 3.58  │ 2.9  │ 4.7  │

julia> append!(m, df[2,:])
1x4 DataFrames.DataFrame
│ Row │ row1   │ x3_39 │ x2_5 │ x4_5 │
┝━━━━━┿━━━━━━━━┿━━━━━━━┿━━━━━━┿━━━━━━┥
│ 1   │ "row3" │ 3.58  │ 2.9  │ 4.7  │

julia> m
1x4 DataFrames.DataFrame
│ Row │ row1   │ x3_39 │ x2_5 │ x4_5 │
┝━━━━━┿━━━━━━━━┿━━━━━━━┿━━━━━━┿━━━━━━┥
│ 1   │ "row3" │ 3.58  │ 2.9  │ 4.7  │

[Milan Bouchet-Valat]

Le jeudi 24 mars 2016 à 11:05 -0700, Fred a écrit :
> Thank you very much Milan !
> When I searched a solution in DataFrame documentation I did not found
> the keyword "similar". Is there an equivalent for Julia of this
> website for Perl for example ? 

Well, it's listed here in the brand new documentation site:
http://juliastats.github.io/DataFrames.jl/stable/lib/maintypes/

But maybe it's not easy to find...


Regards

[Fred]

Thank you Milan for this useful link.
This website contains more informations than mine, but it does not seems to contains all the functions available for dataframes. For example I did not manage to find that I have to use append! instead of push! to add a row to a dataframe.

[Tom Short]

Feel free to file issues for missing documentation or (even better) pull requests.

[Fred]

Thank you tshort. Is there a website or email address to post requests concerning documentation ?

[Milan Bouchet-Valat]

Le vendredi 25 mars 2016 à 08:26 -0700, Fred a écrit :
> Thank you tshort. Is there a website or email address to post
> requests concerning documentation ?

Use the GitHub project for that. Note you can make pull requests by
editing the documentation online too.


Regards