Melt Wide data.tables into Long data.tables

Reshapes double and tripple wide data.tables to long data.tables

melt_wide(data, id.vars, new.names)

Arguments

data	The input data.frame
id.vars	ID variables
new.names	The new names for the resulting columns

Value

A long data.table

References

http://stackoverflow.com/a/10170630/1270695

Author

Ananda Mahto

Examples

triplewide <- structure(list(ID = 1:4,
                             w1d1t1 = c(4L, 3L, 2L, 2L),
                             w1d1t2 = c(5L, 4L, 3L, 3L),
                             w1d2t1 = c(6L, 5L, 5L, 4L),
                             w1d2t2 = c(5L, 4L, 5L, 2L),
                             w2d1t1 = c(6L, 5L, 4L, 3L),
                             w2d1t2 = c(5L, 4L, 5L, 5L),
                             w2d2t1 = c(6L, 3L, 6L, 3L),
                             w2d2t2 = c(7L, 4L, 3L, 2L)),
                             .Names = c("ID", "w1d1t1", "w1d1t2",
                             "w1d2t1", "w1d2t2", "w2d1t1", "w2d1t2",
                             "w2d2t1", "w2d2t2"),
                             class = "data.frame",
                             row.names = c(NA, -4L))
triplewide
#>   ID w1d1t1 w1d1t2 w1d2t1 w1d2t2 w2d1t1 w2d1t2 w2d2t1 w2d2t2
#> 1  1      4      5      6      5      6      5      6      7
#> 2  2      3      4      5      4      5      4      3      4
#> 3  3      2      3      5      5      4      5      6      3
#> 4  4      2      3      4      2      3      5      3      2
triplewide.long <- melt_wide(triplewide, id.vars="ID",
                            new.names=c("week", "day", "trial"))
triplewide.long
#>     ID variable value week day trial
#>  1:  1   w1d1t1     4    1   1     1
#>  2:  2   w1d1t1     3    1   1     1
#>  3:  3   w1d1t1     2    1   1     1
#>  4:  4   w1d1t1     2    1   1     1
#>  5:  1   w1d1t2     5    1   1     2
#>  6:  2   w1d1t2     4    1   1     2
#>  7:  3   w1d1t2     3    1   1     2
#>  8:  4   w1d1t2     3    1   1     2
#>  9:  1   w1d2t1     6    1   2     1
#> 10:  2   w1d2t1     5    1   2     1
#> 11:  3   w1d2t1     5    1   2     1
#> 12:  4   w1d2t1     4    1   2     1
#> 13:  1   w1d2t2     5    1   2     2
#> 14:  2   w1d2t2     4    1   2     2
#> 15:  3   w1d2t2     5    1   2     2
#> 16:  4   w1d2t2     2    1   2     2
#> 17:  1   w2d1t1     6    2   1     1
#> 18:  2   w2d1t1     5    2   1     1
#> 19:  3   w2d1t1     4    2   1     1
#> 20:  4   w2d1t1     3    2   1     1
#> 21:  1   w2d1t2     5    2   1     2
#> 22:  2   w2d1t2     4    2   1     2
#> 23:  3   w2d1t2     5    2   1     2
#> 24:  4   w2d1t2     5    2   1     2
#> 25:  1   w2d2t1     6    2   2     1
#> 26:  2   w2d2t1     3    2   2     1
#> 27:  3   w2d2t1     6    2   2     1
#> 28:  4   w2d2t1     3    2   2     1
#> 29:  1   w2d2t2     7    2   2     2
#> 30:  2   w2d2t2     4    2   2     2
#> 31:  3   w2d2t2     3    2   2     2
#> 32:  4   w2d2t2     2    2   2     2
#>     ID variable value week day trial
data.table::dcast(triplewide.long, ID + week + day ~ trial)
#>     ID week day 1 2
#>  1:  1    1   1 4 5
#>  2:  1    1   2 6 5
#>  3:  1    2   1 6 5
#>  4:  1    2   2 6 7
#>  5:  2    1   1 3 4
#>  6:  2    1   2 5 4
#>  7:  2    2   1 5 4
#>  8:  2    2   2 3 4
#>  9:  3    1   1 2 3
#> 10:  3    1   2 5 5
#> 11:  3    2   1 4 5
#> 12:  3    2   2 6 3
#> 13:  4    1   1 2 3
#> 14:  4    1   2 4 2
#> 15:  4    2   1 3 5
#> 16:  4    2   2 3 2