[R編程：創建配對的元素

我有元素的列表清單說：[R編程：創建配對的元素

l <- c("x","ya1","xb3","yb3","ab","xc3","y","xa1","yd4")

出這份名單的，我想使匹配X，Y對的列表，即

(("xa1" "ya1") ("xb3" "yb3") ("x" "y"))

從本質上說，我需要捕捉的X元素，在Y元素，然後將它們配對起來：我知道該怎麼做了X，Y提取部分：

xelems <- grep("^x", l, perl=TRUE, value=TRUE) 
yelems <- grep("^y", l, perl=TRUE, value=TRUE)

了一個Y元素的X元素對當

1. xElem == yElem # if xElem and yElem are one char long, i.e. 'x' and 'y'  
2. substr(xElem,1,nchar(xElem)) == substr(yElem,1,nchar(yElem))

沒有秩序的，即匹配xElem和yElem可以定位在任何位置。

但是我不太確定下一部分。我比較熟悉的SKILL programming language（技能是一個LISP衍生物），這是我寫的：

procedure(get_xy_pairs(inputList "l") 
    let((yElem (xyPairs nil) xList yList) 
    xList=setof(i inputList rexMatchp("^x" i)) 
    yList=setof(i inputList rexMatchp("^y" i)) 
    when(xList && yList 
     unless(length(xList)==length(yList) 
    warn("xList and yList mismatch : %d vs %d\n" length(xList) length(yList)) 
    ) 
     foreach(xElem xList 
     if(xElem=="x" 
      then yElem="y" 
      else yElem=strcat("y" substring(xElem 2 strlen(xElem))) 
     ) 
     if(member(yElem yList) 
      then xyPairs=cons(list(xElem yElem) xyPairs) 
      else warn("x element %s has no matching y element \n" xElem) 
     ) 
    ) 
    ) 
    xyPairs 
) 
)

當L RUN，這將返回

get_xy_pairs(l) 
*WARNING* x element xc3 has no matching y element 
(("xa1" "ya1") ("xb3" "yb3") ("x" "y"))

正如我還是新R，如果你們可以幫忙，我會很感激。此外，我確實瞭解R族人傾向於避免循環，並且更傾向於lapply？

Thx提前。 Riad。

來源

2013-12-20 Riad

也許這樣的事情會工作。（只有在你的樣本數據進行測試）

## Remove any item not starting with x or y 
l2 <- l[grepl("^x|^y", l)] 

## Split into a list of items starting with x 
## and items starting with y 
L <- split(l2, grepl("^x", l2)) 

## Give "names" to the "starting with y" group 
names(L[[1]]) <- gsub("^y", "x", L[[1]]) 

## Use match to match the names in the y group with 
## the values from the x group. This results in a 
## nice named vector with the pairs you want 
Matches <- L[[1]][match(L[[2]], names(L[[1]]), nomatch=0)] 
Matches 
#  x xb3 xa1 
# "y" "yb3" "ya1"

作爲data.frame：

MatchesDF <- data.frame(x = names(Matches), y = unname(Matches)) 
MatchesDF 
#  x y 
# 1 x y 
# 2 xb3 yb3 
# 3 xa1 ya1

來源

2013-12-20 02:44:33 A5C1D2H2I1M1N2O1R2T1

阿南達，非常感謝你的解決方案，完美的作品！ – Riad

我將存儲在元組的列表，即：

xypairs 
[[1]] 
[1] "x" "y" 

[[2]] 
[2] "xb3" "yb3"

你的程序也可以與match和substring簡化。

xends <- substring(xelems, 2) 
yends <- substring(yelems, 2) 
ypaired <- match(xends, yends) # Indices of yelems that match xelems 

# Now we need to handle the no-matches: 
xsorted <- c(xelems, rep(NA, sum(is.na(ypaired)))) 
ysorted <- yelems[ypaired] 
ysorted <- c(ysorted, yelems[!(yelems %in% ysorted)]) 

# Now we create the list of tuples: 
xypairs <- lapply(1:length(ysorted), function(i) { 
    c(xsorted[i], ysorted[i]) 
})

結果：

xypairs 
[[1]] 
[1] "x" "y" 

[[2]] 
[1] "xb3" "yb3" 

[[3]] 
[1] "xc3" NA 

[[4]] 
[1] "xa1" "ya1" 

[[5]] 
[1] NA "yd4"

來源

2013-12-20 02:02:37

Manetheran，THX很多關於你的貢獻，非常感謝！ – Riad

[R編程：創建配對的元素

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