ggplot2: One legend with two visual properties derived from common variable

ggplot2: One legend with two visual properties derived from common variable

References

Reference NO 1

http://stackoverflow.com/questions/15188964/ggplot2-one-legend-with-two-visual-properties-derived-from-common-variable

Reference NO 2

http://stackoverflow.com/questions/2954115/irrelevant-legend-information-in-ggplot2

Reference NO 3

http://cran.r-project.org/web/packages/ggplot2/ggplot2.pdf

Reference NO 4

http://www.springer.com/cda/content/document/cda_downloaddocument/9780387981406-c1.pdf?SGWID=0-0-45-766402-p173897424

Reference NO 5

http://moderngraphics11.pbworks.com/f/ggplot2-Book09hWickham.pdf

Reference NO 6

http://vita.had.co.nz/papers/ggplot2-wires.pdf

Reference NO 7

http://imdevsoftware.wordpress.com/tag/ggplot2/

Reference NO 8

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