ddply +汇总功能列名称输入 [英] ddply + summarise function column name input

问题描述

我正在尝试从plyr包中一起使用ddply和summarise，但是在解析不断变化的列名时遇到了困难...在我的示例中，我希望以编程方式在X1中进行解析比在X1中将硬编码编码到ddply函数中.

I am trying to use ddply and summarise together from the plyr package but am having difficulty parsing through column names that keep changing...In my example i would like something that would parse in X1 programatically rather than hard coding in X1 into the ddply function.

设置示例

require(xts)
require(plyr)
require(reshape2)
require(lubridate)
t <- xts(matrix(rnorm(10000),ncol=10), Sys.Date()-1000:1)
t.df <- data.frame(coredata(t))
t.df <- cbind(day=wday(index(t), label=TRUE, abbr=TRUE), t.df)
t.df.l <- melt(t.df, id.vars=c("day",colnames(t.df)[2]), measure.vars=colnames(t.df)[3:ncol(t.df)])

这是我在努力挣扎的一点....

This is the bit im am struggling with....

cor.vars <- ddply(t.df.l, c("day","variable"), summarise, cor(X1, value))

我不想使用术语X1，而是想使用

i do not want to use the term X1 and would like to use something like

cor.vars <- ddply(t.df.l, c("day","variable"), summarise, cor(colnames(t.df)[2], value))

但是出现错误:Error in cor(colnames(t.df)[2], value) : 'x' must be numeric

我还尝试了其他各种组合，这些组合分析了cor中x参数的向量值...但是由于某些原因，它们似乎都不起作用...

I also tried various other combos that parse in the vector values for the x argument in cor...but for some reason none of them seem to work...

有什么想法吗?

推荐答案

尽管这可能不是summarize的预期用法，并且必须有更好的解决方法，但直接的问题答案是使用get:

Although this is probably not the intended usage for summarize and there must be much better approaches to your problem, the direct answer to your question is to use get:

ddply(t.df.l, c("day","variable"), summarise, cor(get(colnames(t.df)[2]), value))

例如，在我看来，这是一种更适合您的问题的方法:

here is for example one approach that is in my opinion better suited to your problem:

ddply(t.df.l, c("day", "variable"), function(x)cor(x["X1"], x["value"]))

以上，"X1"也可以替换为2或包含"X1"的变量的名称，依此类推.这取决于您要如何以编程方式访问该列.

Above, "X1" can be also replaced by 2 or the name of a variable holding "X1", etc. It depends how you want to programmatically access the column.

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