學習筆記，僅供參考，有錯必糾，按需更新

PS：大量參考R的幫助文檔，照搬英文不翻譯

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subset函數

所在包：base

描述

Return subsets of vectors, matrices or data frames which meet conditions.

使用

subset(x, ...)## Default S3 method: subset(x, subset, ...)## S3 method for class 'matrix' subset(x, subset, select, drop = FALSE, ...)## S3 method for class 'data.frame' subset(x, subset, select, drop = FALSE, ...)

參數

參數解釋

x	object to be subsetted
subset	logical expression indicating elements or rows to keep: missing values are taken as false.
select	expression, indicating columns to select from a data frame
drop	passed on to [ indexing operator.

舉個例子

我們利用鳶尾花數據集iris來做這個實驗，首先選擇Species等于 “setosa” 且 Petal.Length 小于1.5的樣本，只返回Sepal.Length, Petal.Length, Species列：

data("iris")testdf <- subset(iris, Species == "setosa" & Petal.Length < 1.5, select = c(Sepal.Length, Petal.Length, Species)) testdf

輸出：

Sepal.Length Petal.Length Species 1 5.1 1.4 setosa 2 4.9 1.4 setosa 3 4.7 1.3 setosa 5 5.0 1.4 setosa 7 4.6 1.4 setosa 9 4.4 1.4 setosa 13 4.8 1.4 setosa 14 4.3 1.1 setosa 15 5.8 1.2 setosa 17 5.4 1.3 setosa 18 5.1 1.4 setosa 23 4.6 1.0 setosa 29 5.2 1.4 setosa 34 5.5 1.4 setosa 36 5.0 1.2 setosa 37 5.5 1.3 setosa 38 4.9 1.4 setosa 39 4.4 1.3 setosa 41 5.0 1.3 setosa 42 4.5 1.3 setosa 43 4.4 1.3 setosa 46 4.8 1.4 setosa 48 4.6 1.4 setosa 50 5.0 1.4 setosa

總結

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