如何使用R dataframe/data.table展开单个列，

library(tidyr)

# 创建一个示例数据框
df <- data.frame(ID = c(1, 2, 3),
                 A = c(10, 20, 30),
                 B = c(100, 200, 300),
                 C = c(1000, 2000, 3000))

# 使用gather()函数展开单个列
df_long <- gather(df, key = "Column", value = "Value", -ID)

library(tidyr)

# 创建一个示例数据框
df_long <- data.frame(ID = c(1, 1, 2, 2, 3, 3),
                      Column = c("A", "B", "A", "B", "A", "B"),
                      Value = c(10, 100, 20, 200, 30, 300))

# 使用spread()函数展开单个列
df_wide <- spread(df_long, key = Column, value = Value)