Creates an Exact_Strategy for exact, score-1.0 token-set matching. Hand it
to the same verbs you would hand a search_strategy(): detect_duplicates()
to group identical records within a table, search_candidates() to match
them across tables. Both return the usual result with score == 1.0.
Two records link only when every column's token set is equal within the same block. This is the same as a fuzzy score of exactly 1.0, reached without any scoring or threshold, and it is robust to empty columns: two records with identical names and both streets blank will link, where a weighted threshold would silently reject them. (A blank column drags a weighted score below its threshold, since its weight stays in the denominator; exact matching has no such ceiling.)
Use it as the cheap first stage of a staged workflow (exact first, then fuzzy
on whatever is left): the leftover records come from extract_unmatched(),
and multi_stage_dedup() / multi_stage_search() thread them through for
you when you pass list(exact_strategy(...), search_strategy(...)).
Usage
exact_strategy(
...,
block_by = NULL,
rarity = "inverse_freq",
containment = c("off", "forward", "bidirectional"),
min_base_rarity = 0,
min_containment_tokens = 1
)Arguments
- ...
Two-sided formulas
column ~ step1 + step2, identical in form tosearch_strategy().- block_by
Optional character vector of blocking columns.
- rarity
Character scalar rarity metric, used only by the
min_base_raritycontainment guard to measure how much identifying weight a base record's tokens carry. One of"inverse_freq"(default),"smoothed_inverse_freq","tfidf", or"bm25"; seesearch_strategy()for what each formula does. Plain equality and forward containment without amin_base_rarityfloor never consult it, so the default is almost always fine.- containment
One of
"off"(set-equality, default),"forward"(link when the base record's tokens are a subset of the target's), or"bidirectional"(either direction). Whether it helps depends on the data; it over-links on noisy corpora, so it is never the default.- min_base_rarity
Numeric containment guard: drop links whose base record carries summed rarity mass below this floor. Default
0.- min_containment_tokens
Numeric containment guard, default
1(no restriction). A proper containment link (one record's tokens a strict subset of the other's) requires the contained record to hold at least this many tokens; set-equality always links. Raise to2to stop a single generic token - a bare category or hub name (e.g. a shopping-centre name) - being a subset of every richer "Store + Centre" name and transitively chaining unrelated records into one entity. Ignored whencontainment = "off".
Examples
# Link only workshops whose name tokens are identical within the same area
# and trade. No threshold to tune, and blank columns do not sink a match.
ex <- exact_strategy(
workshop ~ normalize_text() + word_tokens(min_nchar = 3),
block_by = c("postcode_area", "trade")
)
dups <- detect_duplicates(workshop_register, id = "reg_no", strategy = ex)
head(dups)
#> # A tibble: 6 × 18
#> id duplicate_group score rank workshop proprietor trade legal_form
#> <chr> <int> <dbl> <int> <chr> <chr> <chr> <chr>
#> 1 GMC-00034 34 1 1 Davenport W… Arthur Da… Wood… Sole Trad…
#> 2 GMC-D0014 34 1 2 Davenport W… Arthur Da… Wood… Sole Trad…
#> 3 GMC-00044 44 1 1 Wetherell W… Graham We… Wood… Ltd
#> 4 GMC-D0022 44 1 2 Wetherell W… Graham We… Wood… Ltd
#> 5 GMC-00045 45 1 1 Stark Cabin… Miles Sta… Cabi… LLP
#> 6 GMC-D0026 45 1 2 Stark Cabin… Miles Sta… Cabi… LLP
#> # ℹ 10 more variables: postcode_area <chr>, town <chr>, address <chr>,
#> # established <int>, employees <dbl>, apprentices <dbl>, guild_member <lgl>,
#> # sic <chr>, true_entity <chr>, gen_tier <chr>