R 在每个包含模式的字符串之前在向量中插入字符串

发布于03月31日

我有以下向量:

test <- c("here is some text", "here is some other text", "here is my formula", "2+2", "here is my second formula", "4+4", "here is even more text", "here is my final formula", "6+6")

我希望做的是获取一个包含"FORMULA"的字符串的每个实例，并在其前面插入一个类似"ccc"的随机字符串，这样我就会得到如下所示:

test <- c("here is some text", "here is some other text", "CCC", "here is my formula", "2+2", "CCC", "here is my second formula", "4+4", "here is even more text", "CCC", "here is my final formula", "6+6")

推荐答案

它们仅使用碱基R:

1)使用append，如下所示:

test2 <- test
ix <- rev(grep("formula", test)) - 1
for(i in ix) test2 <- append(test2, "CCC", i)
test2
##  [1] "here is some text"         "here is some other text"  
##  [3] "CCC"                       "here is my formula"       
##  [5] "2+2"                       "CCC"                      
##  [7] "here is my second formula" "4+4"                      
##  [9] "here is even more text"    "CCC"                      
## [11] "here is my final formula"  "6+6"

这里有三个不同的俏皮话.

第一个创建一个矩阵，其第一行包含"ccc"和NA元素，第二行为test.然后它会解开这一点，并移除NA.

第二个迭代测试，如果元素中不包含公式或后跟元素的向量"ccc"，则输出该元素.这将生成一个未列出的列表.

第三个代码在任何包含公式的元素前面加上"ccc\n"，然后将其拆分.

# 2a
c(na.omit(c(rbind(ifelse(grepl("formula", test), "CCC", NA), test))))

# 2b
unlist(lapply(test, function(x) if (grepl("formula", x)) c("CCC", x) else x))

# 2c
scan(text = sub("(.*formula)", "CCC\n\\1", test), what="", quiet=TRUE, sep="\n")