data.table不再通过引用更新 [英] data.table not updating by reference anymore

问题描述

这里是一个函数

f <- function(orderData){
        colNames <- paste0("lim_",sort(unique(orderData[,XLM])))
        orderData[, (colNames):={lim_=factor(XLM);lapply(data.table(model.matrix(~ lim_:w_qalim + 0)), cumsum)}]
}

>

and some sample data

dt = data.table(XLM=sample(1L:300L,5e4,T), w_qalim=sample(1L:5L,5e4,T))
dt1 = data.table(XLM=sample(1L:300L,1e2,T), w_qalim=sample(1L:5L,1e2,T))

执行 f（dt）不更新 dt 通过引用在我的框，但 f（dt1）做。是否为 datatable.alloccol

Executing f(dt) does not update dt by reference on my box but f(dt1) do. Is it expected/ something to do with datatable.alloccol

推荐答案

两种情况下，数据表的长度为2并且长度为100：

In both cases the length of the data table is 2 and the truelength is 100:

> length(dt); truelength(dt)
[1] 2
[1] 100
> length(dt1); truelength(dt1)
[1] 2
[1] 100

，在 dt colNames 的情况下为300，所以2 + 300超过了长度，但是在 dt1 colNames 是81所以2 + 81不。

however, in the case of dt colNames is 300 so 2+300 exceeds the truelength but in the case of dt1 colNames is 81 so 2+81 does not.

可以预先分配更大的长度，例如

You can either allocate a larger truelength in advance, e.g.

alloc.col(dt, 1000)

或者您可以设置默认值，以便所有数据表都有较大的默认值：

or you can set the default so that all data tables have a larger default:

options(datatable.alloccol = 1000)

请参阅？alloc.col ，

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