Cookbook - Using more complex recipes involving text
Emil Hvitfeldt
2022-05-04
Source:vignettes/cookbook---using-more-complex-recipes-involving-text.Rmd
cookbook---using-more-complex-recipes-involving-text.RmdWorking 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 the 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.
Counting select words
Sometimes it is enough to know the counts of a handful of specific words. This can be easily be achieved by 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
#> <dbl> <dbl> <dbl>
#> 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
#> # … with 4,274 more rowsRemoving words in addition to the stop words list
You 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
#> # … with 4,274 more rows, and 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>, …Letter distributions
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
#> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 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
#> # … with 4,274 more rows, and 20 more variables: tf_medium_g <dbl>,
#> # tf_medium_h <dbl>, tf_medium_i <dbl>, tf_medium_j <dbl>,
#> # tf_medium_k <dbl>, tf_medium_l <dbl>, tf_medium_m <dbl>,
#> # tf_medium_n <dbl>, tf_medium_o <dbl>, tf_medium_p <dbl>,
#> # tf_medium_q <dbl>, tf_medium_r <dbl>, tf_medium_s <dbl>,
#> # tf_medium_t <dbl>, tf_medium_u <dbl>, tf_medium_v <dbl>,
#> # tf_medium_w <dbl>, tf_medium_x <dbl>, tf_medium_y <dbl>, …TF-IDF of ngrams of stemmed tokens
Sometimes fairly complicated computations. 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 a option in most other libraries. But the modularity of textrecipes makes this task fairly easy.
First we will tokenize according to words, then stemming those words. We will then paste together the stemmed tokens using step_untokenize so we are back at string 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 …` `tfidf_medium_…` `tfidf_medium_…` `tfidf_medium_…`
#> <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
#> # … with 4,274 more rows, and 495 more variables:
#> # `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>,
#> # `tfidf_medium_2 photograph black` <dbl>, …