在R中的data.table内部运行函数 [英] Run a function inside data.table in R

问题描述

我在R中有一些data.table格式的数据，我需要运行一些功能。

Hi I have some data in data.table format in R and I need to run some function.

假设我有一个名为A的data.table，带有列

Let say I have a data.table called A with columns, "name" "height", "weight".

我想运行一些函数，即data.table中的线性回归并将系数RMSE存储到表中结果。

I want to run some function, i.e. linear regression within data.table and store the coefficients, RMSE into the table results.

A[, .(beta = lm(height ~ weight)$coefficients[2], RMSE = 
     as.numeric(sqrt(crossprod(lm(height 
     ~ weight)$residuals)/(length(lm(height ~ weight)$residuals)- 
     (length(coef(lm(height ~ weight)))-1)))*100),
     by=.(name)]

我的问题：是否有一种方法可以将lm（height〜weight）结果保存为一个对象，然后访问该对象的数据，因此data.table不需要在这里像4次一样运行lm函数？

My question: Is there a way to save the lm(height ~ weight) result as an object and then access this object's data so data.table don't need to run the lm function like 4 times in here?

这可以运行，但是与我使用foreach并循环遍历名称相比，它有点慢，因为我有数百万行数据。

This runs but it is a bit too slow compared to me using foreach and loop over "name" as I have millions rows of data.

谢谢。

推荐答案

通过使用Henrik建议的匿名正文，我可以加快流程！

By using anonymous body as suggested by Henrik, I am able to speed up the process!

A[, {model <- lm(height ~ weight)
       BETA <- model$coefficient[2]
       RMSE <- as.numeric(sqrt(crossprod(model$residuals)/(length(model$residuals)- 
               (length(coef(model))-1)))*100)

       list(BETA = BETA, RMSE = RMSE)
       },
 by = .(name)]

显然，匿名主体（lambda）不需要名称，就像一次运行就忘记了。在此lambda中， lm（）函数运行一次（每个组），并将结果存储在对象中。

Apparently, an anonymous body (lambda) does not require a name and it is like "run once and forget". Inside this lambda, the lm() function is ran once (per group), and the result stored in an object.

然后我们可以从模型对象中提取所需的数据，最后提供 list（）来让 j 将提取的数据转换为列。

We can then extract the required data from the model object and lastly list() is provided to let j convert the extracted data into columns.

非常感谢！

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