Last updated: 2023-11-02

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Rmd 5acae29 Dave Tang 2023-11-02 Text mining using the tm package

The tm package is a framework for text mining applications within R.

library(tm)
Loading required package: NLP
packageVersion("tm")
[1] '0.7.11'

Getting started

The crude corpus:

This data set holds 20 news articles with additional meta information from the Reuters-21578 data set. All documents belong to the topic crude dealing with crude oil.

data(crude)
class(crude)
[1] "VCorpus" "Corpus" 

inspect can be used to display detailed information on a corpus, a term-document matrix, or a text document.

inspect(crude[1:3])
<<VCorpus>>
Metadata:  corpus specific: 0, document level (indexed): 0
Content:  documents: 3

$`reut-00001.xml`
<<PlainTextDocument>>
Metadata:  15
Content:  chars: 527

$`reut-00002.xml`
<<PlainTextDocument>>
Metadata:  15
Content:  chars: 2634

$`reut-00004.xml`
<<PlainTextDocument>>
Metadata:  15
Content:  chars: 330

Create a Term Document Matrix.

tdm <- TermDocumentMatrix(crude)
tdm
<<TermDocumentMatrix (terms: 1266, documents: 20)>>
Non-/sparse entries: 2255/23065
Sparsity           : 91%
Maximal term length: 17
Weighting          : term frequency (tf)

Convert to matrix.

crude_matrix <- as.matrix(tdm)
dim(crude_matrix)
[1] 1266   20

Check out the matrix. We need to remove the symbols!

crude_matrix[1:6, 1:6]
            Docs
Terms        127 144 191 194 211 236
  ...          0   0   0   0   0   0
  "(it)        0   0   0   0   0   0
  "demand      0   1   0   0   0   0
  "expansion   0   0   0   0   0   0
  "for         0   0   0   0   0   0
  "growth      0   0   0   0   0   0

Sparsity is the number of zeros, i.e., words that are not present in documents.

prop.table(table(crude_matrix == 0))

     FALSE       TRUE 
0.08906003 0.91093997 

Functions that can be used on a TermDocumentMatrix.

methods(class = "TermDocumentMatrix")
 [1] [                     as.DocumentTermMatrix as.TermDocumentMatrix
 [4] c                     dimnames<-            Docs                 
 [7] findAssocs            findMostFreqTerms     inspect              
[10] nDocs                 nTerms                plot                 
[13] print                 t                     Terms                
[16] tm_term_score        
see '?methods' for accessing help and source code

Clean corpus.

clean_corpus <- function(x){
  x |>
    tm_map(removePunctuation) |>
    tm_map(stripWhitespace) |>
    tm_map(content_transformer(function(x) iconv(x, to='UTF-8', sub='byte'))) |>
    tm_map(removeNumbers) |>
    tm_map(removeWords, stopwords("en")) |>
    tm_map(content_transformer(tolower)) |>
    tm_map(removeWords, c("etc","ie", "eg", stopwords("english")))
}

tdm <- TermDocumentMatrix(clean_corpus(crude))

crude_matrix <- as.matrix(tdm)
crude_matrix[1:6, 1:6]
           Docs
Terms       127 144 191 194 211 236
  abdulaziz   0   0   0   0   0   0
  ability     0   2   0   0   0   3
  able        0   0   0   0   0   0
  abroad      0   0   0   0   0   1
  accept      0   0   0   0   0   0
  accord      0   0   0   0   0   0

findFreqTerms finds frequent terms in a document-term or term-document matrix.

findFreqTerms(x = tdm, lowfreq = 10)
 [1] "barrel"     "barrels"    "bpd"        "crude"      "dlrs"      
 [6] "government" "industry"   "kuwait"     "last"       "market"    
[11] "meeting"    "minister"   "mln"        "new"        "official"  
[16] "oil"        "one"        "opec"       "pct"        "price"     
[21] "prices"     "production" "reuter"     "said"       "saudi"     
[26] "sheikh"     "will"       "world"     

Limit matrix to specific words.

inspect(
  x = DocumentTermMatrix(
    x = crude,
    list(dictionary = c("government", "market", "official")
    )
  )
)
<<DocumentTermMatrix (documents: 20, terms: 3)>>
Non-/sparse entries: 15/45
Sparsity           : 75%
Maximal term length: 10
Weighting          : term frequency (tf)
Sample             :
     Terms
Docs  government market official
  144          0      3        0
  236          0      0        5
  237          5      0        0
  242          0      1        1
  246          6      0        0
  248          0      4        1
  273          0      1        4
  349          0      1        2
  352          0      1        1
  704          0      1        0

findAssocs finds associations in a document-term or term-document matrix.

findAssocs(x = tdm, terms = 'government', corlimit = 0.8)
$government
agriculture       early    positive         say       years       since 
       1.00        1.00        1.00        0.91        0.83        0.82 

Simple analysis on the matrix.

Most common words.

head(sort(rowSums(crude_matrix), decreasing = TRUE))
   oil   said prices   opec    mln   last 
    85     73     48     42     31     24 

Correlation.

cor(crude_matrix[,1], crude_matrix[,2])
[1] 0.351976

Clustering.

set.seed(31)
my_cluster <- kmeans(x = t(crude_matrix), centers = 4)
my_cluster$cluster
127 144 191 194 211 236 237 242 246 248 273 349 352 353 368 489 502 543 704 708 
  4   3   4   4   4   3   2   4   1   3   3   4   4   4   4   4   4   4   4   4 

Check headings of cluster 3.

meta(crude, 'heading')[my_cluster$cluster == 3]
$`144`
[1] "OPEC MAY HAVE TO MEET TO FIRM PRICES - ANALYSTS"

$`236`
[1] "KUWAIT SAYS NO PLANS FOR EMERGENCY OPEC TALKS"

$`248`
[1] "SAUDI ARABIA REITERATES COMMITMENT TO OPEC PACT"

$`273`
[1] "SAUDI FEBRUARY CRUDE OUTPUT PUT AT 3.5 MLN BPD"

sessionInfo()
R version 4.3.2 (2023-10-31)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 22.04.3 LTS

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3 
LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.20.so;  LAPACK version 3.10.0

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

time zone: Etc/UTC
tzcode source: system (glibc)

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] tm_0.7-11       NLP_0.2-1       workflowr_1.7.1

loaded via a namespace (and not attached):
 [1] jsonlite_1.8.7    compiler_4.3.2    promises_1.2.1    Rcpp_1.0.11      
 [5] slam_0.1-50       xml2_1.3.5        stringr_1.5.0     git2r_0.32.0     
 [9] parallel_4.3.2    callr_3.7.3       later_1.3.1       jquerylib_0.1.4  
[13] yaml_2.3.7        fastmap_1.1.1     R6_2.5.1          knitr_1.45       
[17] tibble_3.2.1      rprojroot_2.0.3   bslib_0.5.1       pillar_1.9.0     
[21] rlang_1.1.1       utf8_1.2.4        cachem_1.0.8      stringi_1.7.12   
[25] httpuv_1.6.12     xfun_0.40         getPass_0.2-2     fs_1.6.3         
[29] sass_0.4.7        cli_3.6.1         magrittr_2.0.3    ps_1.7.5         
[33] digest_0.6.33     processx_3.8.2    rstudioapi_0.15.0 lifecycle_1.0.3  
[37] vctrs_0.6.4       evaluate_0.22     glue_1.6.2        whisker_0.4.1    
[41] fansi_1.0.5       rmarkdown_2.25    httr_1.4.7        tools_4.3.2      
[45] pkgconfig_2.0.3   htmltools_0.5.6.1