Left 與 Right 連接

R 的 data.table 資料合併

Scott Ritchie

Postdoctoral Researcher in Systems Genomics

Left join

將右側 data.table 的資訊加入左側 data.table

merge(x = demographics, y = shipping, by = "name", all.x = TRUE)

Right join

將左側 data.table 的資訊加入右側 data.table

merge(x = demographics, y = shipping, by = "name", all.y = TRUE)

Right 與 Left 等價關係

# Right join
merge(x = demographics, y = shipping, by = "name", all.y = TRUE)

# Same as
merge(x = shipping, y = demographics, by = "name", all.x = TRUE)

預設值

在 merge() 中，all、all.x、all.y 的預設值都是 FALSE
使用 help("merge") 查詢函式參數的預設值

練習說明

將 shipping 與 demographics 做 Left join：

merge(demographics, shipping, by = "name", all.x = TRUE)

將 shipping 與 demographics 做 Right join：

merge(demographics, shipping, by = "name", all.y = TRUE)

一起來練習吧！

R 的 data.table 資料合併