Convert data between wide and long forms

Source: R/long_wide.R

Analogous function for dcast and melt in data.table

wider_dt(data, group, class_to_spread, value_to_spread = NULL, fill = NA)

longer_dt(
  data,
  group,
  gather_class = "class",
  gather_value = "value",
  na.rm = FALSE
)

Arguments

data

data.table
group

The unchanged group in the transformation
class_to_spread

The class of variable to spread
value_to_spread

The value of variable to spread. If missing, will guess automatically.
fill

Value with which to fill missing cells. Default uses NA.
gather_class

The column name of gathered class.
gather_value

The column name of gathered value.
na.rm

If TRUE, entries with NA values will be removed from the data.table.

Value

data.table

Details

In the nest_dt, the data would be nested to a column named `ndt`, which is short for nested data.table.

See also

dcast,melt,dcast

pivot_longer,pivot_wider

Examples

stocks = data.frame(
  time = as.Date('2009-01-01') + 0:9,
  X = rnorm(10, 0, 1),
  Y = rnorm(10, 0, 2),
  Z = rnorm(10, 0, 4)
)

stocks %>%
  longer_dt(time) -> longer_stocks

longer_stocks
#>           time class        value
#>  1: 2009-01-01     X  0.747176602
#>  2: 2009-01-02     X -0.934819658
#>  3: 2009-01-03     X -0.466620448
#>  4: 2009-01-04     X -0.857190403
#>  5: 2009-01-05     X -1.524744178
#>  6: 2009-01-06     X  1.969424843
#>  7: 2009-01-07     X  0.463174707
#>  8: 2009-01-08     X -0.856152426
#>  9: 2009-01-09     X  0.648043285
#> 10: 2009-01-10     X  0.075803960
#> 11: 2009-01-01     Y  0.983522881
#> 12: 2009-01-02     Y -1.507081412
#> 13: 2009-01-03     Y  0.698054706
#> 14: 2009-01-04     Y -0.341697944
#> 15: 2009-01-05     Y  3.262412014
#> 16: 2009-01-06     Y -1.565412083
#> 17: 2009-01-07     Y -0.005787252
#> 18: 2009-01-08     Y  0.826478585
#> 19: 2009-01-09     Y  1.448866904
#> 20: 2009-01-10     Y  4.707889541
#> 21: 2009-01-01     Z -1.125798739
#> 22: 2009-01-02     Z -1.924185745
#> 23: 2009-01-03     Z  0.316903698
#> 24: 2009-01-04     Z  3.079441321
#> 25: 2009-01-05     Z  2.253347839
#> 26: 2009-01-06     Z -1.495950095
#> 27: 2009-01-07     Z -2.405222236
#> 28: 2009-01-08     Z -1.696700139
#> 29: 2009-01-09     Z -3.489263524
#> 30: 2009-01-10     Z  0.426738459
#>           time class        value

longer_stocks %>%
  wider_dt(time,class)
#>           time           X            Y          Z
#>  1: 2009-01-01  0.74717660  0.983522881 -1.1257987
#>  2: 2009-01-02 -0.93481966 -1.507081412 -1.9241857
#>  3: 2009-01-03 -0.46662045  0.698054706  0.3169037
#>  4: 2009-01-04 -0.85719040 -0.341697944  3.0794413
#>  5: 2009-01-05 -1.52474418  3.262412014  2.2533478
#>  6: 2009-01-06  1.96942484 -1.565412083 -1.4959501
#>  7: 2009-01-07  0.46317471 -0.005787252 -2.4052222
#>  8: 2009-01-08 -0.85615243  0.826478585 -1.6967001
#>  9: 2009-01-09  0.64804329  1.448866904 -3.4892635
#> 10: 2009-01-10  0.07580396  4.707889541  0.4267385

longer_stocks %>%
  mutate_dt(one = 1) %>%
  wider_dt(time,class,one)
#>           time X Y Z
#>  1: 2009-01-01 1 1 1
#>  2: 2009-01-02 1 1 1
#>  3: 2009-01-03 1 1 1
#>  4: 2009-01-04 1 1 1
#>  5: 2009-01-05 1 1 1
#>  6: 2009-01-06 1 1 1
#>  7: 2009-01-07 1 1 1
#>  8: 2009-01-08 1 1 1
#>  9: 2009-01-09 1 1 1
#> 10: 2009-01-10 1 1 1