选择R中向量中的特定元素

Question

我有一个矢量， myvector <- c("a","b","c","cat","4","dog","cat","f")。我想选择那些紧跟在包含字符串＆＃34; cat＆＃34;的元素之后的元素。

即，我希望myvector2仅包含＆＃34; 4＆＃34;和＆＃34; f＆＃34;。我不知道从哪里开始。

Answer 1

myvector <- c("a","b","c","cat","4","dog","cat","f")

where_is_cat <- which(myvector == "cat")
# [1] 4 7

myvector[where_is_cat + 1]
# [1] "4" "f"

myvector2 <- myvector[where_is_cat + 1]

Answer 2

试试这个：

x[grep('cat',x)+1]
#[1] "4" "f"

Answer 3

您可以通过索引来减去第一个元素（list[-1]）的子集列表，其中列表减去其最后一个元素（list[-length(list)]）等于＆＃34; cat＆＃34;

list[-1][list[-length(list)]=="cat"]
# [1] "4" "f"