melt : Wide to Long spread || cast : Long to Wide spread (R)

Data files are mostly structured in a format to be optimized for less storage rather than exploration friendly and we need to re-structure it for ease of exploratory analysis.

Either Data will be stored Wide Spread : variables in Columns  OR Long Spread: variables in Rows

Wide Spread:  Data is arranged horizontally  (variables Column – wise)

            

Long Spread : Data is arranged Vertically (variables Row-wise)

For Exploratory Analysis, we often need to Transpose (or flip) data other way around. Reshape2 package provides “melt” and “cast” to transpose data effectively.

1     1)       melt : Wide spread to Long Spread

Lets say Population and Area for a City is present in Columns and requirement is to convert them Row-wise.

Data Creation:

Ø  city = data.frame( “City”                        = c ( "Delhi", "London", "New York"),

                                "Population.Mn"  = c ( 44.30, 31.36, 40.42),

                                   "Area.SqKm"       = c ( 77.13, 90.05, 80.00)

                               )

Using melt to transpose data Population and Area to rows

Ø  m =  melt(city)

 m

                

Or

Melt provides further options to specify id columns and explicitly provide name for variable column.

Ø  mt = melt (city , id.vars = c ("City")

                                           , variable_name = "Attribute"   )

    mt

 2) Cast : Long spread to Wide Spread

Ø  c = cast(m)

c

Or
we can explicitly define Id and value variables

Ø  ct = cast (mt

                                      , City ~  Attribute

                                    , value.var = c ( "Population.Mn", "Area.SqKm") )

                  ct

Cheers!!