R: find corpus document by ID-tag and set an additional tag

Question

Want to write tags for documents being inside a corpus. The tags are stored outside the corpus in a dataframe with the specific unique document-IDs.

The challenge: (1) take each ID from the dataframe, (2) find the coresponding document inside the corpus, (3) set the tag from the dataframe to the corpus document with the specific ID.

library("tm")
someID <- paste(letters[1:15], 16:30, sep="")
someTag <- sample(c("a","x","g","h","e"), 15, replace=TRUE)

data(crude) # a corpus with 20 docs
meta(crude, type="local", tag="someID") <- someID  # adding some additional IDs to the corpus

mydf <- data.frame(cbind(someTag, someID))  # Creating a dataframe with similar IDs
mydf <- mydf[sample(nrow(mydf)),]  # permutation of elements (rows)
rownames(mydf) <- 1:15  # overwriting the rownames

############################################
# doesn't work - my try - pseudocode

for (i in 1:nrow(mydf)){
          meta(crude[which(crude$someID==mydf$someID[i])], tag="someTag", type="local") <- mydf$someTag[i]
    }

############################################
# How the data looks like:

mydf
# R output:
> mydf
   someTag someID
1        h    l27
2        x    g22
3        h    d19
4        a    e20
5        h    i24
6        x    j25
7        h    o30
8        x    n29
9        e    h23
10       x    m28
11       h    k26
12       e    c18
13       a    a16
14       e    b17
15       x    f21

meta(crude[1], type="local")
# R output:
> meta(crude[1], type="local")
Available meta data pairs are:
  Author       : 
  DateTimeStamp: 1987-02-26 17:00:56
  Description  : 
  Heading      : DIAMOND SHAMROCK (DIA) CUTS CRUDE PRICES
  ID           : 127
  Language     : en
  Origin       : Reuters-21578 XML
User-defined local meta data pairs are:
$TOPICS
[1] "YES"

$LEWISSPLIT
[1] "TRAIN"

$CGISPLIT
[1] "TRAINING-SET"

$OLDID
[1] "5670"

$Topics
[1] "crude"

$Places
[1] "usa"

$People
character(0)

$Orgs
character(0)

$Exchanges
character(0)

$someID
[1] "a16"

Thank you for any help (;

Answer 1

According to ?meta

meta(crude, type="local", tag="someID") <- someID

will assign the meta data tag someID at the individual document level. What you want is to create a tagging at the collection level. For this, you want to manipulate the DMetaData attribute of the corpus crude. You can do this as:

meta(crude, type="indexed", tag="someID") <- someID

but I find it much easier to use the access

DMetaData(crude)$someID  <- someID

(this at least works for corpora of type VCorpus). With this adjustment:

library("tm")
someID <- paste(letters[1:15], 16:30, sep="")
someTag <- sample(c("a","x","g","h","e"), 15, replace=TRUE)

data(crude) # a corpus with 20 docs
# Need to be sure to allocate full tag and id set.
DMetaData(crude)$someID <- c(someID,rep(NA,5))
DMetaData(crude)$someTag <- rep(NA,20)

mydf <- data.frame(cbind(someTag, someID), stringsAsFactors=FALSE)  # Creating a dataframe with similar IDs
mydf <- mydf[sample(nrow(mydf)),]  # permutation of elements (rows)
rownames(mydf) <- 1:15  # overwriting the rownames

for (i in 1:nrow(mydf)){
      DMetaData(crude)$someTag[DMetaData(crude)$someID==mydf$someID[i]]<- mydf$someTag[i]
    }

Result:

> DMetaData(crude)
   MetaID someID someTag  
1       0    a16       a
2       0    b17       h
3       0    c18       g
4       0    d19       a
5       0    e20       e
6       0    f21       a
7       0    g22       x
8       0    h23       g
9       0    i24       h
10      0    j25       e
11      0    k26       x
12      0    l27       a
13      0    m28       a
14      0    n29       h
15      0    o30       a
16      0   <NA>    <NA>
17      0   <NA>    <NA>
18      0   <NA>    <NA>
19      0   <NA>    <NA>
20      0   <NA>    <NA>