6.19 长宽转换

args("reshape")

## function (data, varying = NULL, v.names = NULL, timevar = "time", 
##     idvar = "id", ids = 1L:NROW(data), times = seq_along(varying[[1L]]), 
##     drop = NULL, direction, new.row.names = NULL, sep = ".", 
##     split = if (sep == "") {
##         list(regexp = "[A-Za-z][0-9]", include = TRUE)
##     } else {
##         list(regexp = sep, include = FALSE, fixed = TRUE)
##     }) 
## NULL

PlantGrowth 数据集的重塑操作也可以使用内置的函数 reshape() 实现

PlantGrowth$id <- rep(1:10, 3)
dat <- reshape(
  data = PlantGrowth, idvar = "group", v.names = "weight",
  timevar = "id", direction = "wide",
  sep = ""
)
knitr::kable(dat,
  caption = "不同生长环境下植物的干重", row.names = FALSE,
  col.names = gsub("(weight)", "", names(dat)),
  align = "c"
)

表 6.2: 不同生长环境下植物的干重

group	1	2	3	4	5	6	7	8	9	10
ctrl	4.17	5.58	5.18	6.11	4.50	4.61	5.17	4.53	5.33	5.14
trt1	4.81	4.17	4.41	3.59	5.87	3.83	6.03	4.89	4.32	4.69
trt2	6.31	5.12	5.54	5.50	5.37	5.29	4.92	6.15	5.80	5.26

或者，我们也可以使用 tidyr 包提供的 pivot_wider() 函数

tidyr::pivot_wider(
  data = PlantGrowth, id_cols = id,
  names_from = group, values_from = weight
)

## # A tibble: 10 × 4
##       id  ctrl  trt1  trt2
##    <int> <dbl> <dbl> <dbl>
##  1     1  4.17  4.81  6.31
##  2     2  5.58  4.17  5.12
##  3     3  5.18  4.41  5.54
##  4     4  6.11  3.59  5.5 
##  5     5  4.5   5.87  5.37
##  6     6  4.61  3.83  5.29
##  7     7  5.17  6.03  4.92
##  8     8  4.53  4.89  6.15
##  9     9  5.33  4.32  5.8 
## 10    10  5.14  4.69  5.26

或者，我们还可以使用 data.table 包提供的 dcast() 函数，用于将长格式的数据框重塑为宽格式的

PlantGrowth_DT <- as.data.table(PlantGrowth)
# 纵
dcast(PlantGrowth_DT, id ~ group, value.var = "weight")

##     id ctrl trt1 trt2
##  1:  1 4.17 4.81 6.31
##  2:  2 5.58 4.17 5.12
##  3:  3 5.18 4.41 5.54
##  4:  4 6.11 3.59 5.50
##  5:  5 4.50 5.87 5.37
##  6:  6 4.61 3.83 5.29
##  7:  7 5.17 6.03 4.92
##  8:  8 4.53 4.89 6.15
##  9:  9 5.33 4.32 5.80
## 10: 10 5.14 4.69 5.26

# 横
dcast(PlantGrowth_DT, group ~ id, value.var = "weight")

##    group    1    2    3    4    5    6    7    8    9   10
## 1:  ctrl 4.17 5.58 5.18 6.11 4.50 4.61 5.17 4.53 5.33 5.14
## 2:  trt1 4.81 4.17 4.41 3.59 5.87 3.83 6.03 4.89 4.32 4.69
## 3:  trt2 6.31 5.12 5.54 5.50 5.37 5.29 4.92 6.15 5.80 5.26