Working to get textual data converted into numerical can be done in
many different ways. The steps included in textrecipes
should hopefully give you the flexibility to perform most of your
desired text preprocessing tasks. This vignette will showcase examples
that combine multiple steps.
This vignette will not do any modeling with the processed text as its
purpose it to showcase flexibility and modularity. Therefore the only
packages needed will be recipes and
textrecipes. Examples will be performed on the
tate_text data-set which is packaged with
modeldata.
Sometimes it is enough to know the counts of a handful of specific
words. This can be easily achieved using the arguments
custom_stopword_source and keep = TRUE in
step_stopwords.
words <- c("or", "and", "on")
okc_rec <- recipe(~., data = tate_text) %>%
step_tokenize(medium) %>%
step_stopwords(medium, custom_stopword_source = words, keep = TRUE) %>%
step_tf(medium)
okc_obj <- okc_rec %>%
prep()
bake(okc_obj, tate_text) %>%
select(starts_with("tf_medium"))
#> # A tibble: 4,284 × 3
#> tf_medium_and tf_medium_on tf_medium_or
#> <int> <int> <int>
#> 1 1 0 1
#> 2 0 1 0
#> 3 0 1 0
#> 4 0 1 0
#> 5 0 1 0
#> 6 0 1 0
#> 7 0 1 0
#> 8 0 1 0
#> 9 1 1 0
#> 10 0 1 0
#> # ℹ 4,274 more rowsYou might know of certain words you don’t want included which isn’t a
part of the stop word list of choice. This can easily be done by
applying the step_stopwords step twice, once for the stop
words and once for your special words.
stopwords_list <- c(
"was", "she's", "who", "had", "some", "same", "you", "most",
"it's", "they", "for", "i'll", "which", "shan't", "we're",
"such", "more", "with", "there's", "each"
)
words <- c("sad", "happy")
okc_rec <- recipe(~., data = tate_text) %>%
step_tokenize(medium) %>%
step_stopwords(medium, custom_stopword_source = stopwords_list) %>%
step_stopwords(medium, custom_stopword_source = words) %>%
step_tfidf(medium)
okc_obj <- okc_rec %>%
prep()
bake(okc_obj, tate_text) %>%
select(starts_with("tfidf_medium"))
#> # A tibble: 4,284 × 951
#> tfidf_medium_1 tfidf_medium_10 tfidf_medium_100 tfidf_medium_11
#> <dbl> <dbl> <dbl> <dbl>
#> 1 0 0 0 0
#> 2 0 0 0 0
#> 3 0 0 0 0
#> 4 0 0 0 0
#> 5 0 0 0 0
#> 6 0 0 0 0
#> 7 0 0 0 0
#> 8 0 0 0 0
#> 9 0 0 0 0
#> 10 0 0 0 0
#> # ℹ 4,274 more rows
#> # ℹ 947 more variables: tfidf_medium_12 <dbl>, tfidf_medium_13 <dbl>,
#> # tfidf_medium_133 <dbl>, tfidf_medium_14 <dbl>, tfidf_medium_15 <dbl>,
#> # tfidf_medium_151 <dbl>, tfidf_medium_16 <dbl>, tfidf_medium_160 <dbl>,
#> # tfidf_medium_16mm <dbl>, tfidf_medium_18 <dbl>, tfidf_medium_19 <dbl>,
#> # tfidf_medium_2 <dbl>, tfidf_medium_20 <dbl>, tfidf_medium_2000 <dbl>,
#> # tfidf_medium_201 <dbl>, tfidf_medium_21 <dbl>, tfidf_medium_22 <dbl>, …Another thing one might want to look at is the use of different
letters in a certain text. For this we can use the built-in character
tokenizer and keep only the characters using the
step_stopwords step.
okc_rec <- recipe(~., data = tate_text) %>%
step_tokenize(medium, token = "characters") %>%
step_stopwords(medium, custom_stopword_source = letters, keep = TRUE) %>%
step_tf(medium)
okc_obj <- okc_rec %>%
prep()
bake(okc_obj, tate_text) %>%
select(starts_with("tf_medium"))
#> # A tibble: 4,284 × 26
#> tf_medium_a tf_medium_b tf_medium_c tf_medium_d tf_medium_e tf_medium_f
#> <int> <int> <int> <int> <int> <int>
#> 1 1 0 2 3 4 0
#> 2 1 0 1 0 2 0
#> 3 1 0 1 0 2 0
#> 4 1 0 1 0 2 0
#> 5 3 0 1 0 0 0
#> 6 3 0 1 0 0 0
#> 7 3 0 2 0 1 0
#> 8 1 0 1 1 1 0
#> 9 5 0 1 1 0 0
#> 10 1 0 0 0 1 0
#> # ℹ 4,274 more rows
#> # ℹ 20 more variables: tf_medium_g <int>, tf_medium_h <int>, tf_medium_i <int>,
#> # tf_medium_j <int>, tf_medium_k <int>, tf_medium_l <int>, tf_medium_m <int>,
#> # tf_medium_n <int>, tf_medium_o <int>, tf_medium_p <int>, tf_medium_q <int>,
#> # tf_medium_r <int>, tf_medium_s <int>, tf_medium_t <int>, tf_medium_u <int>,
#> # tf_medium_v <int>, tf_medium_w <int>, tf_medium_x <int>, tf_medium_y <int>,
#> # tf_medium_z <int>Sometimes fairly complicated computations are needed. Here we would
like the term frequency inverse document frequency (TF-IDF) of the most
common 500 ngrams done on stemmed tokens. It is quite a handful and
would seldom be included as an option in most other libraries. But the
modularity of textrecipes makes this task fairly easy.
First we will tokenize according to words, then stem those words. We
will then paste together the stemmed tokens using
step_untokenize so we are back at strings that we then
tokenize again but this time using the ngram tokenizers. Lastly just
filtering and tfidf as usual.
okc_rec <- recipe(~., data = tate_text) %>%
step_tokenize(medium, token = "words") %>%
step_stem(medium) %>%
step_untokenize(medium) %>%
step_tokenize(medium, token = "ngrams") %>%
step_tokenfilter(medium, max_tokens = 500) %>%
step_tfidf(medium)
okc_obj <- okc_rec %>%
prep()
bake(okc_obj, tate_text) %>%
select(starts_with("tfidf_medium"))
#> # A tibble: 4,284 × 499
#> `tfidf_medium_100 digit print` tfidf_medium_16 mm bl…¹ tfidf_medium_16 mm p…²
#> <dbl> <dbl> <dbl>
#> 1 0 0 0
#> 2 0 0 0
#> 3 0 0 0
#> 4 0 0 0
#> 5 0 0 0
#> 6 0 0 0
#> 7 0 0 0
#> 8 0 0 0
#> 9 0 0 0
#> 10 0 0 0
#> # ℹ 4,274 more rows
#> # ℹ abbreviated names: ¹`tfidf_medium_16 mm black`,
#> # ²`tfidf_medium_16 mm project`
#> # ℹ 496 more variables: `tfidf_medium_16 mm shown` <dbl>,
#> # `tfidf_medium_16mm shown a` <dbl>, `tfidf_medium_2 aluminium panel` <dbl>,
#> # `tfidf_medium_2 digit print` <dbl>, `tfidf_medium_2 lithograph on` <dbl>,
#> # `tfidf_medium_2 monitor colour` <dbl>, …