循环R数据以生成条件字符串

Question

我有一个R数据，里面有11个代码。我需要运行一个循环或等效，并在每次迭代中动态地生成一个字符串，在每个迭代中，最多有3个代码块被一个+符号隔开。我怎么能这么做？

all_stockticks <-   
data.frame(symbol=c("AAPL","GOOG","MSFT","C","JPM","GS","INFY","WIT","CTSH","V","MA")
)

In iteration-1 output would be str=AAPL+GOOG+MSFT
In iteration-2 output would be str=C+JPM+GS
In iteration-3 output would be str=INFY+WIT+CTSH
In iteration-4 output would be str=V+MA

Answer 1

试试动物园包里的rollapply：

library(zoo)
rollapply(all_stockticks, 3, by = 3, paste, collapse = "+", partial = TRUE, 
            align = "left")

给予：

     symbol          
[1,] "AAPL+GOOG+MSFT"
[2,] "C+JPM+GS"      
[3,] "INFY+WIT+CTSH" 
[4,] "V+MA"    

Answer 2

下面是IRanges的方法：

library(IRanges)
symbolList <- relist(as.character(all_stockticks$symbol),
                     breakInChunks(nrow(all_stockticks), 3))
unstrsplit(symbolList, "+")

breakInChunks函数生成一个表示分区的对象。我们调用relist来形成具有这样一个分区的列表，最后调用unstrsplit (直觉上是strsplit的逆)来折叠字符串。在这里，所有的迭代都是在本机代码中进行的，所以应该是快速的。

Answer 3

你可以用：

 n <- nrow(all_stockticks)
 c(by(all_stockticks[,1], as.numeric(gl(n,3,n)), FUN=paste,collapse="+"))
              1                2                3                4 
 #"AAPL+GOOG+MSFT"       "C+JPM+GS"  "INFY+WIT+CTSH"           "V+MA"