HDBSCAN in token-level clouds

The workflow this package is designed for uses HDBSCAN (Campello, Moulavi, and Sander 2013) to cluster the tokens. The main purpose is to systematically and objectively identify groups of similar tokens, while allowing some of them to be excluded as noise. Montes (2021) argues that the groups identified by HDBSCAN tend to coincide with the groups that a human researcher might visually identify in a t-SNE rendering of the same model with perplexity 30. However, the nature of these clusters is very diverse, leading to a technical classification that can be linked both to visual shapes and linguistic properties (see Chapter 5 of Montes (2021)). The functions in this vignette take output from the semasioFlow Python workflow and from the cloud processing vignette, prepares the data to be used in the Level3 ShinyApp and shows how to classify clouds according to said typology.

Register HDBSCAN

The first step is to decide on which lemmas HDBSCAN will be computed; often you might only be interested in the medoids. HDBSCAN information, from clustering to membership probabilities or \(\varepsilon\) values, could in principle be included for NephoVis, but it would require a lot of adjusting and it’s still on the wishlist.

The current workaround is to leave the HDBSCAN visualization to the Level3 ShinyApp ¹, which requires the output of this step as an RDS file and the type-level distance matrices corresponding to the different models. the file has a named list with one item per lemma, and in each lemma a senses dataframe with token IDs and other general information of interest and, most importantly, a medoidCoords named list with one item per model. Each model object includes:

coords: the coordinates of the tokens, next to other variables in the “variables” dataframe like, in my case, “senses”, as well as the tailored list of context words. summarizeHDBSCAN() adds the HDBSCAN-derived values (cluster, membership and \(\varepsilon\)).
cws: distribution of first-order context words across HDBSCAN clusters and their t-SNE coordinates if available. This dataframe has one row per context word per cluster and recall, precision and F-score information for the relationship between the context word and the HDBSCAN cluster.

Note that, in order to use tailored contexts, they need to already be computed and stored in the '[lemma].variables.tsv' file as shown in vignette('weightConcordance'). The main function, summarizeHDBSCAN(), requires:

lemma
input_dir: the directory where the distance matrices are stored
output_dir: the directory where the output from vignette('processClouds') is stored
coords_name: the infix of the coordinates files

# You could run it on all the models or just the medoids
# models <- read_tsv(file.path(output_dir, lpaste0(lemma, ".models.tsv")))$`_model` # all models
models <- read_tsv(file.path(output_dir, paste0(lemma, ".medoids.tsv")))$medoids # only medoids
res <- map(setNames(models, models),
           summarizeHDBSCAN, lemma = lemma,
           input_dir = input_dir,
           output_dir = output_dir,
           coords_name = '.tsne.30')

# I would normally make one of these files for all my lemmas and store it within the github directory above the lemma subdirectories
to_write <- list()
to_write[lemma] <- res
write_rds(to_write, file.path(output_dir, "hdbscan.rds"))

We can also use purrr::map() to create a named list gathering the full data for each lemma)

lemmas <- c('lemma1', 'lemma2', 'lemma3') #or whatever they are
input_dir <- file.path(base_dir, "output", "tokens") # where the data is stored
output_dir <- file.path(base_dir, "nephovis") # where the data will go

# HDBSCAN ----
map(setNames(lemmas, lemmas), function(lemma){
  models <- read_tsv(file.path(output_dir, paste0(lemma, ".medoids.tsv")))$medoids # only medoids
  map(setNames(models, models),
      summarizeHDBSCAN, lemma = lemma,
      input_dir = file.path(input_dir, lemma),
      output_dir = file.path(output_dir, lemma))
}) %>%
  write_rds(file.path(output_dir, "hdbscan.rds"))

Cloud classification

Running classifyModel() with the path to the distance matrices and the output from the summarizeHDBSCAN() returns a dataframe with one row per model per cluster, summary information related to the HDBSCAN clustering (from \(\varepsilon\) values) and mean distances between tokens to separability indices in relation to the t-SNE rendering. In addition, it uses some of these variables to classify the shapes of the clusters.

With purrr::imap_dfr() we can combine the data across multiple lemmas for an overarching dataframe. Note that the data will correspond to whatever went through summarizeHDBSCAN(): if you would like a classification for all your models, you will need to run summarizeHDBSCAN() on all of them.

models <- readRDS(file.path(output_dir, "hdbscan.rds")) # output of the previous section

# For one model
lname <- names(models)[[1]]
mname <- names(models[[lname]]$medoidCoords)[[1]]

classifyModel(models[[lname]]$medoidCoords[[1]],
             names(models[[lname]]$medoidCoords)[[1]],
             file.path(input_dir, lname))
             
# For all models, all lemmas
classification <- imap_dfr(models, function(ldata, lname){
    imap_dfr(models[[lname]]$medoidCoords, classifyModel,
    ttmx_dir = file.path(input_dir, lname)) %>% 
    mutate(lemma = lname)
})

References

Campello, Ricardo J. G. B., Davoud Moulavi, and Joerg Sander. 2013. “Density-Based Clustering Based on Hierarchical Density Estimates.” In Advances in Knowledge Discovery and Data Mining, edited by Jian Pei, Vincent S. Tseng, Longbing Cao, Hiroshi Motoda, and Guandong Xu, 160–72. Lecture Notes in Computer Science. Berlin, Heidelberg: Springer.

Montes, Mariana. 2021. “Cloudspotting: Visual Analytics for Distributional Semantics.” PhD thesis, Leuven: KU Leuven.

Mariana Montesr

2022-04-04

Register HDBSCAN

Cloud classification

References