R中的目标变量重新编码

Question

我正在尝试进行一些文本处理,需要重新编码句子的单词,以便在新变量中以特定方式识别目标单词.例如,给定一个看起来像这样的数据框......

subj <- c("1", "1", "1", "2", "2", "2", "2", "2")
condition <- c("A", "A", "A", "B", "B", "B", "B", "B")
sentence <- c("1", "1", "1", "2", "2", "2", "2", "2")
word <- c("I", "like", "dogs.", "We", "don't", "like", "this", "song.")
d <- data.frame(subj,condition, sentence, word)

 subj condition sentence  word
 1         A        1     I
 1         A        1     like
 1         A        1     dogs.
 2         B        2     We
 2         B        2     don't
 2         B        2     like
 2         B        2     this
 2         B        2     song.

我需要创建一个新列,其中目标字的每个实例(在此示例中,当d $ word ="like")标记为0,并且句子块中"like"之前的所有单词将减少,并且"之后的所有单词"喜欢"增量.每个主题都有多个句子,句子因条件而异,因此循环需要考虑每个主语,每个句子的目标词的实例.最终结果看起来应该是这样的.

 subj condition sentence  word   position
 1         A        1     I        -1
 1         A        1     like      0
 1         A        1     dogs.     1
 2         B        2     We       -2
 2         B        2     don't    -1
 2         B        2     like      0
 2         B        2     this      1
 2         B        2     song.     2

对不起,如果问题措辞不好,我希望它有意义!请注意,目标不在每个句子中的相同位置(相对于句子的开头).我对R很新,可以弄清楚如何增加或减少,但不能在每个句子块中做两件事.有关最佳方法的任何建议吗？非常感谢!

Answer 1

您可以添加一个索引,然后可以将其用于相对位置.
使用data.table可以sentence很容易地将其分解

library(data.table)
DT <- data.table(indx=1:nrow(d), d, key="indx")

DT[, position:=(indx - indx[word=="like"]), by=sentence]

# Results
DT
#    indx subj condition sentence  word position
# 1:    1    1         A        1     I       -1
# 2:    2    1         A        1  like        0
# 3:    3    1         A        1 dogs.        1
# 4:    4    2         B        2    We       -2
# 5:    5    2         B        2 don't       -1
# 6:    6    2         B        2  like        0
# 7:    7    2         B        2  this        1
# 8:    8    2         B        2 song.        2

UDATE:

如果您的语法不正确,您可能希望使用grepl而不是==

DT[, position:=(indx - indx[grepl("like", word)]), by=sentence]

Answer 2

我认为在文本处理中，明智的做法是避免让文本条目成为因素。在这种情况下，我使用了as.character但我建议设置options(stringsAsFactors=FALSE);

d$position <- with( d, ave(as.character(word), sentence, 
                               FUN=function(x) seq_along(x) - which(x=="like") ) )
> d
  subj condition sentence  word position
1    1         A        1     I       -1
2    1         A        1  like        0
3    1         A        1 dogs.        1
4    2         B        2    We       -2
5    2         B        2 don't       -1
6    2         B        2  like        0
7    2         B        2  this        1
8    2         B        2 song.        2