data.table操作与列名称与空格失败 [英] data.table operations by column name with spaces fails

问题描述

可重现的示例

 ＃使用Iris数据集
库table）
 iris 
 colnames（iris）[3]<  -   - Petal Length
 iris<  -  as.data.table（iris）
 
  
 iris [，Petal.Width] 
  
但是访问名称包含空格的列不起作用
  iris [，Petal Length] 
 iris [，'Petal Length'] 
  
唯一的解决方案似乎是
  iris [，iris $'Petal Length'] 
  
 评论 $ b我是新的data.table。我明白data.table中有很多奇怪的地方;是这一个吗？我会更改我的变量名称以摆脱空格，但我不喜欢如果我不需要。我还读了以前关于列名的问题 - 我知道在最后一个问题更新后的两年里，这是可以看出，当列名没有空格时。 
解决方案
只需使用 with = FALSE  http://datatable.r-forge.r-project.org/datatable-faq.pdf\">data.table常见问题点1.1-1.3和2.17：
  iris [，'Petal Length'，with = FALSE] 
  
 
 $ b b 
，并请务必阅读出色的 data.table PDF小插图和新HTML小插图。
 
 
 
 
 
 
在这种情况下，对于你期望的（向量），使用 [[更合适：
  iris [['Petal Length']] 
  
或者，您还可以引用列名称，如同他们是 j ：
  iris [，`Petal Length`] 
  
 
Reproducible example
#Use the Iris data set
library(data.table)
iris 
colnames(iris)[3] <- "Petal Length"
iris <- as.data.table(iris)
Accessing column without space is fine
iris[,Petal.Width]
however access a column where the name contains a space doesn't work
iris[,Petal Length]
iris[,'Petal Length']
The only solution seems to be
iris[,iris$'Petal Length']
Comments
I'm new to data.table. I understand there's a lot of quirks in data.table; is this one of them? I would change my variable names to get rid of spaces, but I'd prefer not to if i didn't need to. I also read a previous questions regarding just column names - and I understand in the two years since that last question updates have allowed it - this can be seen in the ease when the colname has no spaces. 
解决方案
Just use with = FALSE as explained under data.table FAQ points 1.1-1.3 and 2.17:
iris[ ,'Petal Length', with = FALSE]
and make sure to read the excellent introduction to data.table PDF vignette and the new HTML vignettes.



In this case, for what you expect (a vector), using [[ is more appropriate:
iris[['Petal Length']]
Alternatively, you can also refer to column names as if they were variables in j:
iris[, `Petal Length`] # note the backticks.


                        
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