How to melt and cast dataframes using dplyr?

Question

Recently I am doing all my data manipulations using dplyr and it is an excellent tool for that. However I am unable to melt or cast a data frame using dplyr. Is there any way to

Answer 1

To add to answers above using @Lovetoken's mini_iris example (this is too complex for a comment) - for those newcomers who do not understand what is meant by melt and casting.

library(reshape2)
library(tidyr)
library(dplyr)

# example data : `mini_iris`
mini_iris <- iris[c(1, 51, 101), ]

# mini_iris
#Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
#1            5.1         3.5          1.4         0.2     setosa
#51           7.0         3.2          4.7         1.4 versicolor
#101          6.3         3.3          6.0         2.5  virginica

Melt is taking the dataframe and expanding into a long list of values. Not efficient but can be useful if you need to combine sets of data. Think of the structure of an icecube melting on a tabletop and spreading out.

melted1 <- testiris %>% melt(id.vars = "Species")

> nrow(melted1)
[1] 12

head(melted1)
# Species     variable      value
# 1     setosa Sepal.Length   5.1
# 2 versicolor Sepal.Length   7.0
# 3  virginica Sepal.Length   6.3
# 4     setosa  Sepal.Width   3.5
# 5 versicolor  Sepal.Width   3.2
# 6  virginica  Sepal.Width   3.3

You can see how the data has now been broken into many rows of value. The column names are now text within a variable column.

casting will reassemble back to a data.table or data.frame.