DOC: Revise "Merge, join, and concatenate" doc with graphical examples

[sinhrks]

I think the doc is little difficult for beginners, because examples use slicing to prepare input which cannot imagine immediately.

• http://pandas.pydata.org/pandas-docs/stable/merging.html

The alternative is using diagrams like below. I've prepared a function to output it using #6661, thus it can be generated during the doc build. If looks useful, I'll work on it.

[jorisvandenbossche]

+1 times a lot

See also http://www.rstudio.com/wp-content/uploads/2015/01/data-wrangling-cheatsheet.pdf for some nice examples how it can be explained graphical (they use some colors as wel to indicate where the orignal data ended up in the result)

[jreback]

+1 on this as well
pictures are worth many words!

[jankatins]

Wow, this is great!