筛选R中的数据索引对象中的行

Question

我是R新手。我有一个数据索引的onject，需要过滤以便我可以获取每个第X个数据点。我如何去做这件事？用于创建数据 代码为：

temp <- blpGetData(conn, securities[1], fields=values,start=startdate,end=enddate, barsize=interval, barfields=tick,retval=datatype) 
assign(paste(gsub(" +","",repl[1])),temp) 
name <- paste("merge(",paste(gsub(" +","",repl[1]))) 
suf <- paste(", suffixes=c('.",paste(gsub(" +","",repl[1])),"'",sep="") 

for(i in 2:length(securities)){ 
    temp <- blpGetData(conn, securities[i], 
         fields=values, 
         start=startdate, 
         end=enddate, 
         barsize=interval, 
         barfields=tick, 
         retval=datatype) 
    assign(paste(gsub(" +","",repl[i])),temp) 
    name <- paste(name,",",paste(gsub(" +","",repl[i]))) 
    suf <- paste(suf,",'.",paste(gsub(" +","",repl[i])),"'",sep="") 
} 
name <- paste(name,suf,"))") 
mat <- eval(parse(text=name)) 

我希望每一个X行。 mat是对象。

> cat(name) 
PX_OPEN..CINC1 PX_HIGH..CINC1 PX_LOW..CINC1 PX_LAST..CINC1 PX_OPEN..CINC5 PX_HIGH..CINC5 PX_LOW..CINC5 PX_LAST..CINC5 PX_OPEN..UST10Y PX_HIGH..UST10Y PX_LOW..UST10Y PX_LAST..UST10Y 

> str(mat) ‘zoo’ series from 2011-11-11 to 2012-01-18 
Data: num [1:49, 1:12] 206 205 205 212 219 ... 
- attr(*, "dimnames")=List of 2 
..$ : NULL 
..$ : chr [1:12] "PX_OPEN..CINC1" "PX_HIGH..CINC1" "PX_LOW..CINC1" "PX_LAST..CINC1" 
... Index: Date[1:49], format: "2011-11-11" "2011-11-14" "2011-11-15" "2011-11-16" "2011-11-17" "2011-11-18" ... 

Answer 1

如果您告诉我们您的物体是什么，这将有所帮助。矢量？一个列表？

如果它是一个名为myvector载体，你希望每个x个数据点从第一你可以用seq(...)生成序列1, 1+x, 1+2*x, 1+3*x, ...索引到你的对象开始。请参阅?seq。

如：

myvector <- runif(100) # generate vector of 100 random values 
idx  <- seq(1,length(myvector),by=10) # get every 10th value starting from 
              # & including 1, 
myvector[idx] # every 10th value: elements 1, 11, 21, ... 

UPDATE

因为你的对象是二维的，请尝试：

n <- 5 # get every 5th object 
idx <- seq(1,nrow(mat),by=n) 
mat[idx,]