描述

    通过增加列数和减少行数，将data_frame从长格式转换为宽格式。

    长表变宽表 - 图1

    1. stocks = data.frame(
    2.   time = as.Date('2009-01-01') + 0:9,
    3.   X = rnorm(10, 0, 1),
    4.   Y = rnorm(10, 0, 2),
    5.   Z = rnorm(10, 0, 4)
    6. ) %>%
    7.   longer_dt(time) -> longer_stocks
    8. longer_stocks
    10. longer_stocks %>%
    11.   wider_dt("time",
    12.            name = "name",
    13.            value = "value")
    15. longer_stocks %>%
    16.   mutate_dt(one = 1) %>%
    17.   wider_dt("time",
    18.            name = "name",
    19.            value = "one")
    20. ## using "fun" parameter for aggregation
    21. DT <- data.table(v1 = rep(1:2, each = 6),
    22.                  v2 = rep(rep(1:3, 2), each = 2),
    23.                  v3 = rep(1:2, 6),
    24.                  v4 = rnorm(6))
    25. ## for each combination of (v1, v2), add up all values of v4
    26. DT %>%
    27.   wider_dt(v1,v2,
    28.            value = "v4",
    29.            name = ".",
    30.            fun = sum)