DOC: warning about copying for df.append/concat. Fixes #7967

closes #7967 
No worries, formatting *is* important. Thanks for the tips, hopefully this
should do it.

On Mon, Oct 6, 2014 at 11:53 AM, jreback <notifications@github.com> wrote:

> In doc/source/merging.rst:
>
> > @@ -100,6 +98,17 @@ means that we can now do stuff like select out each chunk by key:
> >  It's not a stretch to see how this can be very useful. More detail on this
> >  functionality below.
> >
> > +.. note::
> > +  It is worth noting however, that ``concat`` (and therefore ``append``) makes
> > +  a full copy of the data, and that constantly reusing this function can
> > +  create a signifcant performance hit. If you need to use the operation over
> > +  several datasets, use a list comprehension.
> > +
> > +.. ipython:: python
>
> this should be a code-block (we don't want to evaluate it), just show it
>
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> <https://github.com/pydata/pandas/pull/8488/files#r18468838>.
>