r - 在数据表中查找数据并将其添加到新列

Question

我有两个数据表，如下所示:
二元组

 w1w2           freq   w1          w2      
 common names   1      common      names  
 department of  4      department  of  
 family name    6      family      name  

bigrams = setDT(structure(list(w1w2 = c("common names", "department of", "family name"
), freq = c(1L, 4L, 6L), w1 = c("common", "department", "family"
), w2 = c("names", "of", "name")), .Names = c("w1w2", "freq", 
"w1", "w2"), row.names = c(NA, -3L), class = "data.frame"))

一元语法

w1            freq  
common        2  
department    3  
family        4  
name          5  
names         1  
of            9  

unigrams = setDT(structure(list(w1 = c("common", "department", "family", "name", 
"names", "of"), freq = c(2L, 3L, 4L, 5L, 1L, 9L)), .Names = c("w1", 
"freq"), row.names = c(NA, -6L), class = "data.frame"))

所需输出

 w1w2           freq   w1          w2      w1freq    w2freq  
 common names   1      common      names   2         1
 department of  4      department  of      3         9
 family name    6      family      name    4         5

到目前为止我做了什么

setkey(bigrams, w1)
setkey(unigrams, w1)
result <- bigrams[unigrams]

这为我提供了 w1 的 i.freq 列，但是当我尝试对 w2 执行相同操作时，i.freq 列出现了。 freq 列已更新以反射(reflect) w2 的频率。

如何在单独的列中获取 w1 和 w2 的频率？

注意:我已经看到了 data.table Lookup value and translate 的解决方案和 Modify column of a data.table based on another column and add the new column

Answer 1

您可以执行两次联接，并且在 data.table v1.9.6 中，您可以为不同的列名称指定 on= 参数。

library(data.table)

bigrams[unigrams, on=c("w1"), nomatch = 0][unigrams, on=c(w2 = "w1"), nomatch = 0]

            w1w2 freq         w1    w2 i.freq i.freq.1
1:   family name    6     family  name      4        5
2:  common names    1     common names      2        1
3: department of    4 department    of      3        9