Added ggplot2 transformation support for plot_nns_ratio

[xiliny]

Dear authors,

In submitting this pull request, I added a new argument called scale_transform to plot_nns_ratio, which specifies the ggplot2 transformation of the x axis. I tested the changes with the following code (largely based on example(plot_nns_ratio)):

Example (click to expand)

library(ggplot2)
library(quanteda)
library(conText)

# tokenize corpus
toks <- tokens(cr_sample_corpus)

# build a tokenized corpus of contexts sorrounding a target term
immig_toks <- tokens_context(x = toks, pattern = "immigration", window = 6L)

# sample 100 instances of the target term, stratifying by party (only for example purposes)
set.seed(2022L)
immig_toks <- tokens_sample(immig_toks, size = 100, by = docvars(immig_toks, 'party'))

# we limit candidates to features in our corpus
feats <- featnames(dfm(immig_toks))

# compute ratio
set.seed(2022L)
immig_nns_ratio <- get_nns_ratio(x = immig_toks,
                                 N = 10,
                                 groups = docvars(immig_toks, 'party'),
                                 numerator = "R",
                                 candidates = feats,
                                 pre_trained = cr_glove_subset,
                                 transform = TRUE,
                                 transform_matrix = cr_transform,
                                 bootstrap = TRUE,
                                 # num_bootstraps should be at least 100,
                                 # we use 10 here due to CRAN-imposed constraints
                                 # on example execution time
                                 num_bootstraps = 100,
                                 permute = FALSE,
                                 num_permutations = 10,
                                 verbose = FALSE)

plot_nns_ratio(x = immig_nns_ratio, alpha = 0.01, horizontal = FALSE, scale_transform = "identity")
ggsave("vertical-identity.png")
plot_nns_ratio(x = immig_nns_ratio, alpha = 0.01, horizontal = TRUE, scale_transform = "identity")
ggsave("horizontal-identity.png")
plot_nns_ratio(x = immig_nns_ratio, alpha = 0.01, horizontal = FALSE, scale_transform = "log")
ggsave("vertical-log.png")
plot_nns_ratio(x = immig_nns_ratio, alpha = 0.01, horizontal = TRUE, scale_transform = "log")
ggsave("horizontal-log.png")

Here are the resulting plots

scale_transform	horizonal=TRUE	horizonal=FALSE
"identity"
"log"

This is just a basic implementation. Let me know if you want me to make any further changes!

[prodriguezsosa]

Thanks @xiliny, code looks good. Question: what's the motivation for using a log transform here?