quanteda：具有新文本和旧词汇的 dtm

Question

我使用 quanteda 构建文档术语矩阵：

library(quanteda)
mytext = "This is my old text"
dtm <- dfm(mytext, tolower=T)
convert(dtm,to="data.frame")

产生：

  doc_id this is my old text
1  text1    1  1  1   1    1

我需要使“新”文本（新语料库）适合我现有的 dtm（使用相同的词汇表以便出现相同的矩阵列）

假设我的“新”text/corpus 是：

newtext = "This is my new text"

如何将这个“新”text/corpus 与现有的 dtm 词汇表相匹配，以便获得如下矩阵：

  doc_id this is my old text
1  text1    1  1  1   0    1

Answer 1

您需要 dfm_match()，然后再转换为 data.frame。

library(quanteda)
## Package version: 2.1.2

mytext <- c(oldtext = "This is my old text")
dtm_old <- dfm(mytext)
dtm_old
## Document-feature matrix of: 1 document, 5 features (0.0% sparse).
##          features
## docs      this is my old text
##   oldtext    1  1  1   1    1

newtext <- c(newtext = "This is my new text")
dtm_new <- dfm(newtext)
dtm_new
## Document-feature matrix of: 1 document, 5 features (0.0% sparse).
##          features
## docs      this is my new text
##   newtext    1  1  1   1    1

为了匹配它们，使用 dfm_match() 使新的 dfm 符合旧的功能集和顺序：

dtm_matched <- dfm_match(dtm_new, featnames(dtm_old))
dtm_matched
## Document-feature matrix of: 1 document, 5 features (20.0% sparse).
##          features
## docs      this is my old text
##   newtext    1  1  1   0    1

convert(dtm_matched, to = "data.frame")
##    doc_id this is my old text
## 1 newtext    1  1  1   0    1

quanteda：具有新文本和旧词汇的 dtm

quanteda: dtm with new text and old vocabulary

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