Compare Subsequence Patterns Between Groups

Extracts all k-gram patterns (subsequences of length k) from sequences in each group, computes standardized residuals against the independence model, and optionally runs a permutation or chi-square test of group differences.

Usage

sequence_compare(
  x,
  group = NULL,
  sub = 3:5,
  min_freq = 5L,
  test = c("permutation", "chisq", "none"),
  iter = 1000L,
  adjust = "fdr"
)

Arguments

x

A netobject_group (from grouped build_network), a netobject (requires group), or a wide-format data.frame (requires group).

group

Character or vector. Column name or vector of group labels. Not needed for netobject_group.

sub

Integer vector. Pattern lengths to analyze. Default: 3:5.

min_freq

Integer. Minimum frequency in each group for a pattern to be included. Default: 5.

test

Character. Inference method: one of "permutation" (default), "chisq", or "none". See Details.

iter

Integer. Permutation iterations. Only used when test = "permutation". Default: 1000.

adjust

Character. P-value correction method (see p.adjust). Default: "fdr".

Value

An object of class "net_sequence_comparison" containing:

patterns

Tidy data.frame. Always present: pattern, length, freq_<group>, prop_<group>, resid_<group>. If test = "permutation": effect_size, p_value. If test = "chisq": statistic, p_value.

groups

Character vector of group names.

n_patterns

Integer. Number of patterns passing min_freq.

params

List of sub, min_freq, test, iter, adjust.

Details

Standardized residuals are always computed from a 2xG contingency table of (this pattern vs. everything else) using the textbook formula (o - e) / sqrt(e * (1 - r/N) * (1 - c/N)). They describe how much each group's count for a given pattern deviates from expectation under independence, scaled to be approximately N(0,1) under the null.

The optional test argument chooses an inference method:

"permutation"

Shuffles group labels across sequences and recomputes a per-pattern statistic (row-wise Euclidean residual norm). Answers: "is this pattern's distribution associated with group membership at the actor level?" Respects the sequence as the unit of analysis; can be underpowered when the number of sequences is small.

"chisq"

Runs chisq.test on the 2xG table per pattern. Answers: "do the group streams generate this pattern at different rates?" Treats each k-gram occurrence as an event; fast and powerful even with few sequences, but the iid assumption it makes is optimistic when sequences are strongly autocorrelated.

"none"

Skip inference. Only residuals, frequencies, and proportions are returned.

P-values are adjusted once across all patterns (not per-pattern) using any method supported by p.adjust. The default is "fdr" (Benjamini-Hochberg).

Examples

seqs <- data.frame(
  V1 = sample(LETTERS[1:4], 60, TRUE),
  V2 = sample(LETTERS[1:4], 60, TRUE),
  V3 = sample(LETTERS[1:4], 60, TRUE),
  V4 = sample(LETTERS[1:4], 60, TRUE)
)
grp <- rep(c("X", "Y"), 30)
net <- build_network(seqs, method = "relative")
res <- sequence_compare(net, group = grp, sub = 2:3, test = "chisq")