如何使用eval向data.table添加列 [英] How to add columns to data.table using eval
问题描述
我有一个数据表的观察和模型是是和否。为了简单起见,我只假设组。我浪费计算一些分类统计,我想控制选择哪一个。我知道如何使用eval,并将其保存在另一个data.table,但我想添加到现有的data.table,因为我每个组只有一行。
首先,我为每个组创建应急表。
DT categorical< obs == category [1]& mod == category [1]),
b = sum(obs == category [2]& mod == category [1]),
c = sum obs == category [1]& mod == category [2]),
d = sum(obs == category [2]& mod == category [2]),by = groupBy]
然后定义统计
my_exprs = quote(list(
n = a + b + c + d,
s =(a + c)/(a + b + c + d),
r = (a + b)/(a + b + c + d)))
以下行,它将给我一个新的data.table:
statList < - c(n,s )
w = which(names(my_exprs)%in%statList)
categorical [,eval(my_exprs [c(1,w)]),by = groupBy]
如何使用:=在这个例子中,将结果添加到我的旧DT,这里称为分类?我做了以下,并得到错误消息:
分类[,`:=`(eval(my_exprs [c )])),by = groupBy]
在`[.data.table`(分类,,`:=`(eval(my_exprs [c(1,w)] )),:
在`:=`(col1 = val1,col2 = val2,...)形式中,所有参数必须命名
感谢,
我无法重现您的示例,保留 my_exprs
,但定义
my_newcols = as.call在
://stackoverflow.com/questions/22595765/data-table-joins-select-all-columns-in-the-i-argument/22596160#22596160> Arun的回答。
或者,您可以在开始时使用:=
构建表达式:
my_newcols = quote(`:=`(n = a + b + c + d,s = a + c))
pre>
I have a data table of observation and model of being yes and no. For simplicity I have assumed only to groups. I wast to calculate some categorical statistics which I want to have control over which one to be chosen. I know how to do it using eval and save it in another data.table but I want to add to the existing data.table as I have only one row for each group. Could anyone help me?
First I create the contingency table for each group.
DT <- data.table::data.table(obs = rep(c("yes","no"), 5), mod = c(rep("yes",5), rep("no", 5)), groupBy = c(1,1,1,1,1,2,1,1,2,1)) categorical <- DT[, .(a = sum(obs == category[1] & mod == category[1]), b = sum(obs == category[2] & mod == category[1]), c = sum(obs == category[1] & mod == category[2]), d = sum(obs == category[2] & mod == category[2])), by = groupBy]
Then define the statistics
my_exprs = quote(list( n = a+b+c+d, s = (a+c)/(a+b+c+d), r = (a+b)/(a+b+c+d)))
If i use the following lines, it will give me a new data.table:
statList <- c("n","s") w = which(names(my_exprs) %in% statList) categorical[, eval(my_exprs[c(1,w)]), by = groupBy]
How to use := in this example to add the results to my old DT, here called categorical?! I did the following and got error message:
categorical[, `:=`(eval(my_exprs[c(1,w)])), by = groupBy] Error in `[.data.table`(categorical, , `:=`(eval(my_exprs[c(1, w)])), : In `:=`(col1=val1, col2=val2, ...) form, all arguments must be named.
Thanks,
解决方案I cannot reproduce your example, but it might work to keep your
my_exprs
, but definemy_newcols = as.call(c(quote(`:=`), my_exprs))
as in Arun's answer.
Alternately, you could just construct the expression with a
:=
at the start:my_newcols = quote(`:=`(n = a+b+c+d, s = a+c))
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