如何在 r 中的 data.table 中评估(或创建)动态列 [英] How can I evaluate (or create) an on the fly column in data.table in r

问题描述

我想创建一个新的 data.table，或者只是向 data.table 添加一些列.指定多个新列很容易，但是如果我想要第三列根据我正在创建的列之一计算值会发生什么.我认为 plyr 包可以做这样的事情.我们可以在 data.table 中执行这样的迭代(顺序)列创建吗?

I want to create a new data.table or maybe just add some columns to a data.table. It is easy to specify multiple new columns but what happens if I want a third column to calculate a value based on one of the columns I am creating. I think plyr package can do something such as that. Can we perform such iterative (sequential) column creation in data.table?

我想做如下

dt <- data.table(shop = 1:10, income = 10:19*70)
dt[ , list(hope = income * 1.05, hopemore = income * 1.20, hopemorerealistic = hopemore - 100)]  

或许

dt[ , `:=`(hope = income*1.05, hopemore = income*1.20, hopemorerealistic = hopemore-100)]

推荐答案

你也可以在 list 的调用中使用 <- 例如

You can also use <- within the call to list eg

DT <- data.table(a=1:5)


DT[, c('b','d') := list(b1 <- a*2, b1*3)]
DT
   a  b  d
1: 1  2  6
2: 2  4 12
3: 3  6 18
4: 4  8 24
5: 5 10 30

或者

DT[, `:=`(hope = hope <- a+1, z = hope-1)]
DT
   a  b  d hope z
1: 1  2  6    2 1
2: 2  4 12    3 2
3: 3  6 18    4 3
4: 4  8 24    5 4
5: 5 10 30    6 5

这篇关于如何在 r 中的 data.table 中评估(或创建)动态列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！