从data.table的函数创建一个表达式到eval [英] create an expression from a function for data.table to eval
问题描述
给定 data.table
dat:
dat< - data.table(x_one = 1:10,x_two = 1:10,y_one = 1:10,y_two = 1:10)
$ b b
我想要一个函数,在给定root名称的两行之间创建一个表达式,例如 x_one - x_two
。
myfun <
one< - paste0(name,'_one')
two< - paste0(name,'_two')
parse(text = ',two))
}
现在,只使用一个根名称导致向量。
dat [,eval(myfun('x')),]
$ b b [1] 0 0 0 0 0 0 0 0 0 0
使用列表
技术的名称失败:
dat [,list x_out = eval(myfun('x'))),]
eval(expr,envir,enclos)中出错:未找到对象'x_one'
我可以通过添加一个(dat,...)
几乎不会出现data.table-ish
dat [,list(x_out = with(dat,eval(myfun('x' )),
y_out = with(dat,eval(myfun('y'))),]
x_out y_out
1:0 0
2: 0 0
3:0 0
4:0 0
5:0 0
6:0 0
7:0 0
8:0 0
9:0 0
10:0 0
如果有帮助, sessionInfo()
输出低于。我记得能够做到这一点,或者接近它,但它已经一段时间, data.table
更新了...
R版本2.15.1(2012-06-22)
$一个解决方案是将
平台:x86_64-pc-linux-gnu b
$ b locale:
[1] LC_CTYPE = en_US.UTF-8 LC_NUMERIC = C LC_TIME = en_US.UTF-8 LC_COLLATE = en_US.UTF-8
[5] LC_MONETARY = en_US .UTF-8 LC_MESSAGES = en_US.UTF-8 LC_PAPER = C LC_NAME = C
[9] LC_ADDRESS = C LC_TELEPHONE = C LC_MEASUREMENT = zh_US.UTF-8 LC_IDENTIFICATION = C
package:
[1] graphics grDevices utils datasets stats grid methods base
其他附加包:
[1] Cairo_1.5-1 zoo_1.7-7 stringr_0.6.1 doMC_1 .2.5 multicore_0.1-7 iterators_1.0.6 foreach_1.4.0
[8] data.table_1.8.2 circular_0.4-3 boot_1.3-5 ggplot2_0.9.1 reshape2_1.2.1 plyr_1.7.1
通过命名空间加载(并未附加):
[1] codetools_0.2-8 colorspace_1.1-1 dichromat_1.2-4 digest_0.5.2 labeling_0.1 lattice_0.20-6
[ 7] MASS_7.3-20 memoise_0.1 munsell_0.3 proto_0.3-9.2 RColorBrewer_1.0-5 scales_0.2.1
[13] tools_2.15.1
列表(...)
在函数输出中。
我倾向于使用
as.quoted
,从@hadley实现<包中的。()。 library(data.table)
library(plyr)
dat< - data.table(x_one = 1:10,x_two = 1:10,y_one = y_two = 1:10)
myfun < - function(name){
one< - paste0(name,'_one')
two< - paste0(name, )
out < - paste0(name,'_ out')
as.quoted(paste('list(',out,'=',one,' - ',two,')') )[[1]]
}
dat [,eval(myfun('x')),]
#x_out
#1:0
#2:0
#3:0
#4:0
#5:0
#6:0
# 7:0
#8:0
#9:0
#10:0
b $ b一次可以调整您的通话
myfun< - function(name){
one< - paste0(name,'_one')
two< - paste0(name,'_two')
out< - paste0(name,'_ out')
call< - 粘贴(粘贴(输出,'=',一个,' - ',两个),collapse =',')
as.quoted list(',calls,')'))[[1]]
}
dat [,eval(myfun(c('x','y') )),]
#x_out y_out
#1:0 0
#2:0 0
#3:0 0
#4:0 0
#5:0 0
#6:0 0
#7:0 0
#8:0 0
#9:0 0
#0:0 0
至于原因.....
在这个解决方案中,对'
list(..)
的整个调用在作为data.table的parent.frame中进行计算。
[。data.table
中的相关代码为if(missing(j))stop(logical error,j missing)
jsub = substitute(j)
if(is.null ))return(NULL)
jsubl = as.list.default(jsub)
if(identical(jsubl [[1L]],quote(eval))){
jsub = eval
if(is.expression(jsub))jsub = jsub [[1L]]
}
if(在您的情况下)
j = list(xout = eval(myfun('x')))
## then
jsub< - substitute(j)
是
#list(xout = eval(myfun(x)))
和
as.list.default(jsub)
## [[1]]
## list
##
## $ xout
## eval(myfun(x))
code> jsubl [[1L]] 是
列表
,jsubl [[2L]]
是eval(myfun(x))
因此
表
未找到对eval
的调用,因此不会正确处理它。
这将工作,强制正确的data.table中的第二次评估
#using OP myfun
dat [,list(xout = eval(myfun('x'),dat))]
同样的方式
eval(parse(text ='x_one'),dat)
#[1] 1 2 3 4 5 6 7 8 9 10
p>
eval(eval(parse(text ='x_one')),dat)
/ pre>
不
编辑10/4/13
虽然使用
.SD
作为环境可能更安全(但更慢),因为它将对i
或通过
以及例如dat [ ,list(xout = eval(myfun('x'),.SD))]
从马修编辑:
+10到上面。我不能自己更好地解释。再进一步,我有时做的是构建整个 data.table查询,然后
eval
。有时,它可能有点更强大的方式。我想到它喜欢SQL;即,我们经常构造一个发送到SQL服务器来执行的动态SQL语句。当你调试时,有时也更容易看看构造的查询,并在浏览器提示符下运行。但是,有时这样的查询会很长,因此将eval
变成i
,j
或通过
可以更有效地不重新计算其他组件。像往常一样,有很多方法来皮肤的猫。
考虑
eval
整个查询的微妙的原因包括:
分组速度快的一个原因是它检查
j
第一。如果它是一个列表
,它删除名称,但记住他们。然后eval
为每个组的未命名列表,然后在最终结果的末尾重新命名一次。其他方法可能很慢的一个原因是每次重新为每个组重新创建相同的列名向量。更复杂的j
是定义的(例如,如果表达式没有准确地开始list
),内部编码检查逻辑。在这方面有很多测试;例如,结合eval
,以及如果名称丢弃不起作用的冗长报告。但是,构造一个简单查询(完整查询)和eval
,因为这个原因可能会更快更强大。
使用v1.8.2现在优化
j
:选项(datatable.optimize = Inf)
。这将检查j
并修改它以优化mean
和lapply(.SD,.. 。)
idiom,到目前为止。这使得用户需要知道的数量级差异和意味着更少(例如,现在几个wiki点已经消失)。我们可以做更多的这一点;例如DT [a == 10]
可以优化为DT [J(10)]
c $ c> key(DT)[1] ==a [Update Sep 2014 - now implemented in v1.9.3]。但是,如果不是DT [,mean(a),by = b] ,它的
DT [ list(x = eval(expr)),by = b]
其中expr
包含对c $ c>。因此,
eval
整个查询可以用datatable.optimize
更好。如果需要,可以关闭报告中正在进行的操作和优化;例如,以测试其所产生的速度差。
根据注释,FR#2183已添加:更改j = list(xout = eval 。))的eval到在范围内的eval。感谢您的高亮。这是复杂的
j
我的意思是eval
嵌套在表达式中。如果j
开始与eval
,但是,更简单和已经编码
如果有一个外卖,那么它是:do use
DT [...] ,verbose = TRUE]
或选项(datatable.verbose = TRUE)
以检查data.table
在用于涉及eval
的动态查询时仍然有效工作。Given the
data.table
dat:dat <- data.table(x_one=1:10, x_two=1:10, y_one=1:10, y_two=1:10)
I'd like a function that creates an expression between two like rows given their "root" name, e.g.
x_one - x_two
.myfun <- function(name) { one <- paste0(name, '_one') two <- paste0(name, '_two') parse(text=paste(one, '-', two)) }
Now, using just one root name works as expected and results in a vector.
dat[, eval(myfun('x')),] [1] 0 0 0 0 0 0 0 0 0 0
However, trying to assign that output a name using the
list
technique fails:dat[, list(x_out = eval(myfun('x'))),] Error in eval(expr, envir, enclos) : object 'x_one' not found
I can "solve" this by adding a
with(dat, ...)
but that hardly seems data.table-ishdat[, list(x_out = with(dat, eval(myfun('x'))), y_out = with(dat, eval(myfun('y')))),] x_out y_out 1: 0 0 2: 0 0 3: 0 0 4: 0 0 5: 0 0 6: 0 0 7: 0 0 8: 0 0 9: 0 0 10: 0 0
What is the proper way to generate and evaluate these expressions if I want an output like I have above?
In case it helps,
sessionInfo()
output is below. I recall being able to do this, or something close to it, but its been awhile anddata.table
is updated since...R version 2.15.1 (2012-06-22) Platform: x86_64-pc-linux-gnu (64-bit) locale: [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8 [5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8 LC_PAPER=C LC_NAME=C [9] LC_ADDRESS=C LC_TELEPHONE=C LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C attached base packages: [1] graphics grDevices utils datasets stats grid methods base other attached packages: [1] Cairo_1.5-1 zoo_1.7-7 stringr_0.6.1 doMC_1.2.5 multicore_0.1-7 iterators_1.0.6 foreach_1.4.0 [8] data.table_1.8.2 circular_0.4-3 boot_1.3-5 ggplot2_0.9.1 reshape2_1.2.1 plyr_1.7.1 loaded via a namespace (and not attached): [1] codetools_0.2-8 colorspace_1.1-1 dichromat_1.2-4 digest_0.5.2 labeling_0.1 lattice_0.20-6 [7] MASS_7.3-20 memoise_0.1 munsell_0.3 proto_0.3-9.2 RColorBrewer_1.0-5 scales_0.2.1 [13] tools_2.15.1
解决方案One solution is to put the
list(...)
within the function output.I tend to use
as.quoted
, stealing from the way @hadley implements.()
in theplyr
package.library(data.table) library(plyr) dat <- data.table(x_one=1:10, x_two=1:10, y_one=1:10, y_two=1:10) myfun <- function(name) { one <- paste0(name, '_one') two <- paste0(name, '_two') out <- paste0(name,'_out') as.quoted(paste('list(',out, '=',one, '-', two,')'))[[1]] } dat[, eval(myfun('x')),] # x_out # 1: 0 # 2: 0 # 3: 0 # 4: 0 # 5: 0 # 6: 0 # 7: 0 # 8: 0 # 9: 0 #10: 0
To do two columns at once you can adjust your call
myfun <- function(name) { one <- paste0(name, '_one') two <- paste0(name, '_two') out <- paste0(name,'_out') calls <- paste(paste(out, '=', one, '-',two), collapse = ',') as.quoted(paste('list(', calls,')'))[[1]] } dat[, eval(myfun(c('x','y'))),] # x_out y_out # 1: 0 0 # 2: 0 0 # 3: 0 0 # 4: 0 0 # 5: 0 0 # 6: 0 0 # 7: 0 0 # 8: 0 0 # 9: 0 0 # 0: 0 0
As for the reason.....
in this solution the entire call to '
list(..)
is evaluated within the parent.frame being the data.table.The relevant code within
[.data.table
isif (missing(j)) stop("logical error, j missing") jsub = substitute(j) if (is.null(jsub)) return(NULL) jsubl = as.list.default(jsub) if (identical(jsubl[[1L]],quote(eval))) { jsub = eval(jsubl[[2L]],parent.frame()) if (is.expression(jsub)) jsub = jsub[[1L]] }
if (in your case)
j = list(xout = eval(myfun('x'))) ##then jsub <- substitute(j)
is
# list(xout = eval(myfun("x")))
and
as.list.default(jsub) ## [[1]] ## list ## ## $xout ## eval(myfun("x"))
so
jsubl[[1L]]
islist
,jsubl[[2L]]
iseval(myfun("x"))
so
data.table
has not found a call toeval
and will not deal with it appropriately.This will work, forcing the second evaluation within correct data.table
# using OP myfun dat[,list(xout =eval(myfun('x'), dat))]
The same way
eval(parse(text = 'x_one'),dat) # [1] 1 2 3 4 5 6 7 8 9 10
Works but
eval(eval(parse(text = 'x_one')), dat)
Does not
Edit 10/4/13
Although it is probably safer (but slower) to use
.SD
as the environment, as it will then be robust toi
orby
as well egdat[,list(xout =eval(myfun('x'), .SD))]
Edit from Matthew :
+10 to above. I couldn't have explained it better myself. Taking it a step further, what I sometimes do is construct the entire data.table query and then
eval
that. It can be a bit more robust that way, sometimes. I think of it like SQL; i.e, we often construct a dynamic SQL statement that is sent to the SQL server to be executed. When you are debugging, too, it's also sometimes easier to look at the constructed query and run that at the browser prompt. But, sometimes such a query would be very long, so passingeval
intoi
,j
orby
can be more efficient by not recomputing the other components. As usual, many ways to skin the cat.The subtle reasons for considering
eval
ing the entire query include :
One reason grouping is fast is that it inspects the
j
expression first. If it's alist
, it removes the names, but remembers them. It theneval
s an unnamed list for each group, then reinstates the names once, at the end on the final result. One reason other methods can be slow is the recreation of the same column name vector for each and every group, over and over again. The more complexj
is defined though (e.g. if the expression doesn't start precisely withlist
), the harder it gets to code up the inspection logic internally. There are lots of tests in this area; e.g., in combination witheval
, and verbosity reports if name dropping isn't working. But, constructing a "simple" query (the full query) andeval
ing that may be faster and more robust for this reason.With v1.8.2 there's now optimization of
j
:options(datatable.optimize=Inf)
. This inspectsj
and modifies it to optimizemean
and thelapply(.SD,...)
idiom, so far. This makes orders of magnitude difference and means theres less for the user to need to know (e.g. a few of the wiki points have gone away now). We could do more of this; e.g.,DT[a==10]
could be optimized toDT[J(10)]
automatically ifkey(DT)[1]=="a"
[Update Sep 2014 - now implemented in v1.9.3]. But again, the internal optimizations get harder to code up internally if rather thanDT[,mean(a),by=b]
it'sDT[,list(x=eval(expr)),by=b]
whereexpr
contained a call tomean
, for example. Soeval
ing the entire query may play nicer withdatatable.optimize
. Turning verbosity on reports what it's doing and optimization can be turned off if needed; e.g., to test the speed difference it makes.As per comments, FR#2183 has been added: "Change j=list(xout=eval(...))'s eval to eval within scope of DT". Thanks for highlighting. That's the sort of complex
j
I mean where theeval
is nested in the expression. Ifj
starts witheval
, though, that's much simpler and already coded (as shown above) and tested, and should be optimized fine.If there's one take-away from this then it's: do use
DT[...,verbose=TRUE]
oroptions(datatable.verbose=TRUE)
to checkdata.table
is still working efficiently when used for dynamic queries involvingeval
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