data.table自动删除NA中的平均功能？ [英] data.table auto remove NA in by for mean function?

问题描述

今天我在程序中发现了一个错误，因为 data.table auto remove NA for 表示

Today I found out a bug in my program due to data.table auto remove NA for mean

例如：

> a<-data.table(a=c(NA,NA,FALSE,FALSE), b=c(1,1,2,2))
> a

> a[,list(mean(a), sum(a)),by=b]
   b V1 V2
1: 1  0 NA // Why V1 = 0 here? I had expected NA
2: 2  0  0


> mean(c(NA,NA,FALSE,FALSE))
[1] NA
> mean(c(NA,NA))
[1] NA
> mean(c(FALSE,FALSE))
[1] 0

行为？

推荐答案

这不是为了。看起来像是优化问题...

This isn't intended. Looks like a problem with optimization ...

> a[,list(mean(a), sum(a)),by=b]
   b V1 V2
1: 1  0 NA
2: 2  0  0
> options(datatable.optimize=FALSE)
> a[,list(mean(a), sum(a)),by=b]
   b V1 V2
1: 1 NA NA
2: 2  0  0
> 

在v1.8.9中调查和修复，很快就在CRAN。从新闻：

Investigated and fixed in v1.8.9, soon to be on CRAN. From NEWS :

在j中的mean（）已经从v1.8.2开始优化，但是不尊重na.rm = TRUE（默认值）。非常感谢Colin Fang的报告。测试已添加。

mean() in j has been optimized since v1.8.2 but wasn't respecting na.rm=TRUE (the default). Many thanks to Colin Fang for reporting. Test added.

v1.8.2中的新功能为：

The new feature in v1.8.2 was :

mean（）现在自动优化，＃1231。当有大量的组时，这可以加快分组20次。请参阅 wiki点3 ，不再需要知道。通过设置选项（datatable.optimize = 0）关闭优化。

mean() is now automatically optimized, #1231. This can speed up grouping by 20 times when there are a large number of groups. See wiki point 3, which is no longer needed to know. Turn off optimization by setting options(datatable.optimize=0).

这篇关于data.table自动删除NA中的平均功能？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！