Indexing

General rules

The following rules explain target functionality of how getindex, setindex!, and view are intended to work with DataFrame, SubDataFrame and DataFrameRow objects.

The rules for a valid type of index into a column are the following:

• a value, later denoted as col:
  • a Symbol;
  • an Integer that is not Bool;
• a vector, later denoted as cols:
  • a vector of Symbol (does not have to be a subtype of AbstractVector{Symbol});
  • a vector of Integer other than Bool (does not have to be a subtype of AbstractVector{<:Integer});
  • a vector of Bool that has to be a subtype of AbstractVector{Bool}.
  • a colon.

The rules for a valid type of index into a row are the following:

• a value, later denoted as row:
  • an Integer that is not Bool;
• a vector, later denoted as rows:
  • a vector of Integer other than Bool (does not have to be a subtype of AbstractVector{<:Integer});
  • a vector of Bool that has to be a subtype of AbstractVector{Bool};
  • a colon.

In the descriptions below df represents a DataFrame, sdf is a SubDataFrame and dfr is a DataFrameRow.

getindex

The following list specifies return types of getindex operations depending on argument types.

In all operations copying vectors is avoided where possible. If it is performed a description explicitly mentions that the data is copied.

For performance reasons, accessing, via getindex or view, a single row and multiple cols of a DataFrame, a SubDataFrame or a DataFrameRow always returns a DataFrameRow (which is a view-like type).

DataFrame:

• df[col] -> the vector contained in column col;
• df[cols] -> a freshly allocated DataFrame containing the vectors contained in columns cols;
• df[row, col] -> the value contained in row row of column col, the same as df[col][row];
• df[row, cols] -> a DataFrameRow with parent df if cols is a colon and df[cols] otherwise;
• df[rows, col] -> a copy of the vector df[col] with only the entries corresponding to rows selected, the same as df[col][rows];
• df[rows, cols] -> a DataFrame containing copies of columns cols with only the entries corresponding to rows selected.
• @view df[col] -> the vector contained in column col (this is equivalent to df[col]);
• @view df[cols] -> a SubDataFrame with parent df if cols is a colon and df[cols] otherwise;
• @view df[row, col] -> a 0-dimensional view into df[col], the same as view(df[col], row);
• @view df[row, cols] -> a DataFrameRow with parent df if cols is a colon and df[cols] otherwise;
• @view df[rows, col] -> a view into df[col] with rows selected, the same as view(df[col], rows);
• @view df[rows, cols] -> a SubDataFrame with rows selected with parent df if cols is a colon and df[cols] otherwise.

SubDataFrame:

• sdf[col] -> a view of the vector contained in column col of parent(sdf) with DataFrames.rows(sdf) as a selector;
• sdf[cols] -> a SubDataFrame, with parent parent(sdf) if cols is a colon and parent(sdf)[cols] otherwise;
• sdf[row, col] -> a value contained in row row of column col;
• sdf[row, cols] -> a DataFrameRow with parent parent(sdf) if cols is a colon and parent(sdf)[cols] otherwise;
• sdf[rows, col] -> a copy of a vector sdf[col] with only rows rows selected;
• sdf[rows, cols] -> a DataFrame containing columns cols and df[rows, col] as a vector in each col in cols.
• @view sdf[col] -> a view of vector contained in column col of parent(sdf) with DataFrames.rows(sdf) as selector;
• @view sdf[cols] -> a SubDataFrame with parent parent(sdf) if cols is a colon and parent(sdf)[cols] otherwise;
• @view sdf[row, col] -> translates to view(sdf[col], row) (a 0-dimensional view into df[col]);
• @view sdf[row, cols] -> a DataFrameRow with parent parent(sdf) if cols is a colon and parent(sdf)[cols] otherwise;
• @view sdf[rows, col] -> translates to view(sdf[col], rows) (a standard view into sdf[col] vector);
• @view sdf[rows, cols] -> a SubDataFrame with parent parent(sdf) if cols is a colon and sdf[cols] otherwise.

DataFrameRow:

• dfr[col] -> the value contained in column col of dfr;
• dfr[cols] -> a DataFrameRow with parent parent(dfr) if cols is a colon and parent(dfr)[cols] otherwise;
• @view dfr[col] -> a 0-dimensional view into parent(dfr)[DataFrames.row(dfr), col];
• @view dfr[cols] -> a DataFrameRow with parent parent(dfr) if cols is a colon and parent(dfr)[cols] otherwise;

setindex!

Under construction