list 将 lapply 的输出提取到数据帧
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Extracting outputs from lapply to a dataframe
提问by robintw
I have some R code which performs some data extraction operation on all files in the current directory, using the following code:
我有一些 R 代码，它使用以下代码对当前目录中的所有文件执行一些数据提取操作：
files <- list.files(".", pattern="*.tts")
results <- lapply(files, data_for_time, "17/06/2006 12:00:00")
The output from lapply is the following (extracted using dput()) - basically a list full of vectors:
lapply 的输出如下（使用 提取dput()）——基本上是一个充满向量的列表：
list(c("amer", "14.5"), c("appl", "14.2"), c("brec", "13.1"),
c("camb", "13.5"), c("camo", "30.1"), c("cari", "13.8"),
c("chio", "21.1"), c("dung", "9.4"), c("east", "11.8"), c("exmo",
"12.1"), c("farb", "14.7"), c("hard", "15.6"), c("herm",
"24.3"), c("hero", "13.3"), c("hert", "11.8"), c("hung",
"26"), c("lizr", "14"), c("maid", "30.4"), c("mart", "8.8"
), c("newb", "14.7"), c("newl", "14.3"), c("oxfr", "13.9"
), c("padt", "10.3"), c("pbil", "13.6"), c("pmtg", "11.1"
), c("pmth", "11.7"), c("pool", "14.6"), c("prae", "11.9"
), c("ral2", "12.2"), c("sano", "15.3"), c("scil", "36.2"
), c("sham", "12.9"), c("stra", "30.9"), c("stro", "14.7"
), c("taut", "13.7"), c("tedd", "22.3"), c("wari", "12.7"
), c("weiw", "13.6"), c("weyb", "8.4"))
However, I would like to then deal with this output as a dataframe with two columns: one for the alphabetic code ("amer", "appl"etc) and one for the number (14.5, 14.2etc).
不过，我想，然后用此输出与两列的数据帧处理：一个是字母代码（"amer"，"appl"等等），一个用于数字（14.5，14.2等）。
Unfortunately, as.data.framedoesn't seem to work with this input of nested vectors inside a list. How should I go about converting this? Do I need to change the way that my function data_for_timereturns its values? At the moment it just returns c(name, value). Or is there a nice way to convert from this sort of output to a dataframe?
不幸的是，as.data.frame似乎不适用于列表中嵌套向量的这种输入。我应该如何转换这个？我是否需要更改函数data_for_time返回值的方式？目前它刚刚返回c(name, value)。或者有没有一种很好的方法可以将这种输出转换为数据帧？
采纳答案by joran
One option might be to use the ldplyfunction from the plyrpackage, which will stitch things back into a data frame for you.
一种选择可能是使用plyr包中的ldply函数，它将为您将事物拼接回数据框中。
A trivial example of it's use:
它使用的一个简单例子：
ldply(1:10,.fun = function(x){c(runif(1),"a")})
V1 V2
1 0.406373084755614 a
2 0.456838687881827 a
3 0.681300171650946 a
4 0.294320539338514 a
5 0.811559669673443 a
6 0.340881009353325 a
7 0.134072444401681 a
8 0.00850683846510947 a
9 0.326008745934814 a
10 0.90791508089751 a
But note that if you're mixing variable types with c(), you probably willwant to alter your function to return simply data.frame(name= name,value = value)instead of c(name,value). Otherwise everything will be coerced to character (as it is in my example above).
但请注意，如果你是混合变量类型有c()，你可能会想改变你的函数简单地返回data.frame(name= name,value = value)代替c(name,value)。否则一切都会被强制转换为字符（就像我上面的例子一样）。
回答by fotNelton
Try this if resultswere your list:
如果results是你的清单，试试这个：
> as.data.frame(do.call(rbind, results))
V1 V2
1 amer 14.5
2 appl 14.2
3 brec 13.1
4 camb 13.5
...
回答by IRTFM
inp <- list(c("amer", "14.5"), c("appl", "14.2"), .... # did not see need to copy all
data.frame( first= sapply( inp, "[", 1),
second =as.numeric( sapply( inp, "[", 2) ) )
first second
1 amer 14.5
2 appl 14.2
3 brec 13.1
4 camb 13.5
5 camo 30.1
6 cari 13.8
snipped output
回答by Tyler Rinker
Because and forNelton took the response I was in the process of giving and Joran took the only other reasonable response I could think of and since I'm supposed to be writing a paper here's a ridiculous answer:
因为，对于Nelton 采取了我正在给予的回应，而Joran 接受了我能想到的唯一其他合理的回应，而且由于我应该写一篇论文，这里有一个荒谬的答案：
#I named your list LIST
LIST2 <- LIST[[1]]
lapply(2:length(LIST), function(i) {LIST2 <<- rbind(LIST2, LIST[[i]])})
data.frame(LIST2)
