“较长的物体长度不是较短的物体长度的倍数”。 [英] "longer object length is not a multiple of shorter object length"

问题描述

我有此数据集-

print(df)

  object    group   
1 apple      A    
1 banana     B    
1 pear       A    
1 robot      C

print(df2)

  object    group   
1 apple      A    
1 apple      B    
1 apple      A    
1 robot      C
1 robot      C
1 robot      C
1 banana     C

我想计算每个值出现在另一个数据集中的次数，该次数看起来​​完全一样，但是绘制来自不同时间段的数据。另一个数据集称为 df2 。

I'd like to count the number of times each value shows up in another data set, which looks exactly the same but draws data from a different time period. The other dataset is called df2.

我使用了此代码-

x <- df %>%
  mutate(reference = length(df2[df2$object == object,]$object))

它给了我这个错误：较长的对象长度不是较短的对象长度的倍数。

It gave me this error: longer object length is not a multiple of shorter object length.

当我在dplyr之外运行它时，它可以正常工作-

It works when I run this outside of dplyr, like this -

object <- "apple"
length(df2[df2$object == object,]$object)

我可以做这样的相对引用吗，在过滤器中包含 object 吗？

Can I do a relative reference like that, including object in the filter?

推荐答案

根据我的评论：dplyr函数在作为矢量的整个列上工作。尝试

From my comment: dplyr functions work on the whole column taken as a vector. Try

df %>%
rowwise() %>% 
mutate(reference = length(df2[df2$object == object,]$object))%>%
ungroup()

如您所说，除非您计划进行进一步的逐行操作，否则将需要 ungroup 。

As you said, ungroup will be needed, unless you plan on doing further row-wise operations.

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