R如何將列表的一部分轉換爲data.frame？

Question

假設我有一個數據集作爲列表對象。這是一種能快速生成一些隨機數據：

a <- list(x1=rnorm(10),x2=rnorm(10)) 
b <- list(y1=rnorm(10),y2=rnorm(10),y3=rnorm(10)) 
c <- list(x1=rnorm(10),x2=rnorm(10)) 
d <- list(y1=rnorm(10),y2=rnorm(10),y3=rnorm(10)) 
e <- list(x1=rnorm(10),x2=rnorm(10)) 
f <- list(y1=rnorm(10),y2=rnorm(10),y3=rnorm(10)) 
branch1 <- list(a,b) 
branch2 <- list(c,d) 
branch3 <- list(e,f) 
data <- list(branch1,branch2,branch3) 

的數據將是這樣的：

> data 
[[1]] 
[[1]][[1]] 
[[1]][[1]]$x1 
[1] -0.04944765 -2.52337788 0.30997940 -0.71163967 0.48528227 1.17816655 0.84655561 -2.17030509 
[9] -0.03489831 -0.18292103 

[[1]][[1]]$x2 
[1] -0.96112288 -0.57049890 -1.08079903 -3.12189611 0.04508508 -0.38865962 1.61032327 -0.63870639 
[9] 0.77297993 0.48404346 


[[1]][[2]] 
[[1]][[2]]$y1 
[1] 1.1722426 -0.9313285 2.7288262 1.9429077 0.4842252 1.4551183 0.2364701 0.8246233 -0.8540208 
[10] 1.9039492 

[[1]][[2]]$y2 
[1] 1.07758478 -0.90898684 1.00826795 0.97841961 0.70665070 0.05041242 -0.88985476 1.46972378 
[9] -2.38069537 1.87440491 

[[1]][[2]]$y3 
[1] -0.08308981 -0.37208124 0.70363404 -0.88521094 -0.54751152 0.43910681 0.35753713 -0.83412426 
[9] -1.12528856 -1.61850682 



[[2]] 
[[2]][[1]] 
[[2]][[1]]$x1 
[1] 0.01377682 0.19047533 -0.17129543 0.56909904 -0.50928670 1.11754925 0.43099918 -0.37832047 
[9] -0.56111033 0.73358678 

[[2]][[1]]$x2 
[1] 2.3302948 -0.9129171 0.7549973 -1.0379182 -1.9319941 -0.7924752 0.6500014 0.4178630 1.3118695 
[10] -1.2121514 


[[2]][[2]] 
[[2]][[2]]$y1 
[1] 0.8275016 0.7133281 -0.5240551 1.6891841 -0.5621567 -0.7496414 0.5983334 1.3617800 -0.4837031 
[10] 0.4461964 

[[2]][[2]]$y2 
[1] -0.8155957 2.0451346 0.5882782 -0.4417398 -0.2335832 -1.4218698 -1.3949293 0.6129234 -0.6052243 
[10] 0.1414337 

[[2]][[2]]$y3 
[1] -0.3374557 0.3310320 -0.8983646 1.7219435 0.2828211 0.1116751 0.6373569 0.3369811 -1.7301219 
[10] 0.6329963 



[[3]] 
[[3]][[1]] 
[[3]][[1]]$x1 
[1] 0.8392581 -1.0852638 0.2278769 -0.0.1231531 0.7964941 -1.0282257 1.0272565 0.6882902 
[10] 0.2056550 

[[3]][[1]]$x2 
[1] 1.03245491 -0.06994712 -0.53785824 -1.00255262 -0.22105177 -1.07233849 0.93624906 1.03518821 
[9] 1.24065942 -3.51732843 


[[3]][[2]] 
[[3]][[2]]$y1 
[1] -0.30520118 0.60494774 -1.45178410 -0.32739980 -0.15773973 0.76237976 -0.04449191 0.31864511 
[9] -0.12763899 -0.78701147 

[[3]][[2]]$y2 
[1] 0.02523319 1.10718390 -0.24078229 1.44386520 0.52889358 0.04096228 -0.05084876 0.81393090 
[9] 2.14785155 -2.23776686 

[[3]][[2]]$y3 
[1] 2.62345162 -0.07802202 0.12745068 -0.92882646 -0.09972968 0.24213258 0.48338620 0.38180029 
[9] 1.09133254 -0.29834029 

假設我想提取Y1，從每一個列表Y2和Y3，形成一個數據幀如下所示：

ID value1 value2 value3 
    1  y1  y2  y3 
    2  y1  y2  y3 
    3  y1  y2  y3 
    4  y1  y2  y3 
    5  y1  y2  y3 
    6  y1  y2  y3 
...  ... ... ... 

我該怎麼做？

Answer 1

ll <- lapply(data, 
      function(X) data.frame(unlist(X, recursive=FALSE)[c("y1","y2","y3")])) 
df <- do.call(rbind, ll) 

head(df) 
#   y1   y2   y3 
# 1 -1.19755667 0.5993736 -0.385201447 
# 2 -1.58565372 2.1750677 -0.555607218 
# 3 2.06039627 -0.4069106 -0.002523344 
# 4 1.02220253 -0.8521903 -2.247354246 
# 5 -0.05043813 0.2651378 0.114774551 
# 6 1.00512768 -0.7002903 -0.539840393 

要查看（部分），看看在unlist(data[[1]], recursive=FALSE)輸出。

Answer 2

一個是暗示你怎麼可能用它寫遞歸極爲不雅的方式：它是如何工作

extractor <- function(x) { 
    if("y1" %in% names(x)) { 
    x[grepl("y",names(x))] 
    } else { 
    NULL 
    } 
} 
> as.data.frame(unlist(unlist(lapply(data,function(x) lapply(x,extractor)), recursive=FALSE),recursive=FALSE)) 
      y1   y2   y3  y1.1  y2.1  y3.1  y1.2  y2.2  y3.2 
1 0.5500440 0.8009143 0.8641525 1.37000399 -0.2262220 -1.15591653 0.9411658 -1.9429564 0.8993541 
2 1.2366758 1.1652534 -1.1986224 0.67325386 0.3814258 -0.12714861 0.1705881 -0.1163025 -0.8308115 
3 0.1390979 0.3588557 0.6394920 0.07216675 -0.7835158 -1.94151838 -1.0634979 1.1393963 -0.3305447 
4 0.4102751 -0.6085572 2.4302267 -1.50775732 0.5829914 1.18118089 -1.3880490 0.6361240 0.7408145 
5 -0.5584569 -0.2022409 -0.5572155 0.02610023 -1.3165104 1.85991086 2.0867174 -0.4929374 0.9899716 
6 0.6053707 -0.2732481 0.8449042 -0.31641587 -2.8097747 1.07401226 -0.6785031 -0.8341882 -1.9385047 
7 -0.5063335 -0.4686998 -0.7822018 -0.10234651 0.4649680 -0.02734697 -1.8555717 0.2710668 0.1071904 
8 -1.4205655 0.7041673 1.1107114 -1.18155923 0.8405398 -0.03333034 0.5332594 0.1573533 0.6087790 
9 0.1279930 -1.1973635 0.2498247 0.49865804 -0.2858454 -1.51606762 0.3102303 0.6297117 -1.4508243 
10 1.9458512 0.8663661 1.6519154 -1.03895644 0.5041263 0.79038534 -1.3538343 -0.3957980 0.4806256