fuzzylink

The R package fuzzylink implements a probabilistic record linkage procedure proposed in Ornstein (2025). This method allows users to merge datasets with fuzzy matches on a key identifying variable. Suppose, for example, you have the following two datasets:

dfA
#>             name age
#> 1      Joe Biden  81
#> 2   Donald Trump  77
#> 3   Barack Obama  62
#> 4 George W. Bush  77
#> 5   Bill Clinton  77
dfB
#>                         name      hobby
#> 1     Joseph Robinette Biden   Football
#> 2         Donald John Trump        Golf
#> 3       Barack Hussein Obama Basketball
#> 4         George Walker Bush    Reading
#> 5  William Jefferson Clinton  Saxophone
#> 6 George Herbert Walker Bush  Skydiving
#> 7                Biff Tannen   Bullying
#> 8                  Joe Riley    Jogging

We would like a procedure that correctly identifies which records in dfB are likely matches for each record in dfA. The fuzzylink() function performs this record linkage with a single line of code.

library(fuzzylink)
df <- fuzzylink(dfA, dfB, by = 'name', record_type = 'person')
df

#>                A                         B       sim        jw match
#> 1      Joe Biden    Joseph Robinette Biden 0.7661285 0.7673401   Yes
#> 2   Donald Trump        Donald John Trump  0.8388663 0.9333333   Yes
#> 3   Barack Obama      Barack Hussein Obama 0.8457284 0.9200000   Yes
#> 4 George W. Bush        George Walker Bush 0.8445312 0.9301587   Yes
#> 5   Bill Clinton William Jefferson Clinton 0.8730800 0.5788889   Yes
#>   match_probability age      hobby
#> 1                 1  81   Football
#> 2                 1  77       Golf
#> 3                 1  62 Basketball
#> 4                 1  77    Reading
#> 5                 1  77  Saxophone

The procedure works by using pretrained text embeddings to construct a measure of similarity for each pair of names. These similarity measures are then used as predictors in a statistical model to estimate the probability that two name pairs represent the same entity. See Ornstein (2025) for technical details.

Installation

You can install fuzzylink from CRAN with:

install.packages('fuzzylink')

Or you can install the development version from GitHub with:

# install.packages("devtools")
devtools::install_github("joeornstein/fuzzylink")

You will also need API access to a large language model (LLM). The fuzzylink package currently supports both OpenAI and Mistral LLMs, but will default to using OpenAI unless specified by the user.

OpenAI

You will need to create a developer account with OpenAI, and create an API key through their developer platform. For best performance, I strongly recommend purchasing at least $5 in API credits, which will significantly increase your API rate limits.

Once your account is created, copy-paste your API key into the following line of R code.

library(fuzzylink)

openai_api_key('YOUR API KEY GOES HERE', install = TRUE)

Mistral

If you prefer to use language models from Mistral, you can sign up for an account here. As of writing, Mistral requires you to purchase prepaid credits before you can access their language models through the API.

Once you have a paid account, you can create an API key here, and copy-paste the API key into the following line of R code:

library(fuzzylink)

mistral_api_key('YOUR API KEY GOES HERE', install = TRUE)

Now you’re all set up!

Example

Here is some code to reproduce the example above and make sure that everything is working on your computer.

library(tidyverse)
library(fuzzylink)

dfA <- tribble(~name, ~age,
               'Joe Biden', 81,
               'Donald Trump', 77,
               'Barack Obama', 62,
               'George W. Bush', 77,
               'Bill Clinton', 77)

dfB <- tribble(~name, ~hobby,
               'Joseph Robinette Biden', 'Football',
               'Donald John Trump ', 'Golf',
               'Barack Hussein Obama', 'Basketball',
               'George Walker Bush', 'Reading',
               'William Jefferson Clinton', 'Saxophone',
               'George Herbert Walker Bush', 'Skydiving',
               'Biff Tannen', 'Bullying',
               'Joe Riley', 'Jogging')

df <- fuzzylink(dfA, dfB, by = 'name', record_type = 'person')

df

If the df object links all the presidents to their correct name in dfB, everything is running smoothly! (Note that you may see a warning from glm.fit. This is normal. The stats package gets suspicious whenever the model fit is too perfect.)

Arguments

• The by argument specifies the name of the fuzzy matching variable that you want to use to link records. The dataframes dfA and dfB must both have a column with this name.

• The record_type argument should be a singular noun describing the type of entity the by variable represents (e.g. “person”, “organization”, “interest group”, “city”). It is used as part of a language model prompt when training the statistical model.

• The instructions argument should be a string containing additional instructions to include in the language model prompt. Format these like you would format instructions to a human research assistant, including any relevant information that you think would help the model make accurate classifications.

• The model argument specifies which language model to prompt. It defaults to OpenAI’s ‘gpt-4o’, but for simpler problems, you can try ‘gpt-3.5-turbo-instruct’, which will significantly reduce cost and runtime. If you prefer an open-source language model, try ‘open-mixtral-8x22b’.

• The embedding_model argument specifies which pretrained text embeddings to use when modeling match probability. It defaults to OpenAI’s ‘text-embedding-3-large’, but will also accept ‘text-embedding-3-small’ or Mistral’s ‘mistral-embed’.

• Several parameters—including p, k, embedding_dimensions, max_validations, and parallel—are for advanced users who wish to customize the behavior of the algorithm. See the package documentation for more details.

• If there are any variables that must match exactly in order to link two records, you will want to include them in the blocking.variables argument. As a practical matter, I strongly recommend including blocking variables wherever possible, as they reduce the time and cost necessary to compute pairwise distance metrics. Suppose, for example, that our two illustrative datasets have a column called state, and we want to instruct fuzzylink() to only link people who live within the same state.

dfA <- tribble(~name, ~state, ~age,
               'Joe Biden', 'Delaware', 81,
               'Donald Trump', 'New York', 77,
               'Barack Obama', 'Illinois', 62,
               'George W. Bush', 'Texas', 77,
               'Bill Clinton', 'Arkansas', 77)

dfB <- tribble(~name, ~state, ~hobby,
               'Joseph Robinette Biden', 'Delaware', 'Football',
               'Donald John Trump ', 'Florida', 'Golf',
               'Barack Hussein Obama', 'Illinois', 'Basketball',
               'George Walker Bush', 'Texas', 'Reading',
               'William Jefferson Clinton', 'Arkansas', 'Saxophone',
               'George Herbert Walker Bush', 'Texas', 'Skydiving',
               'Biff Tannen', 'California', 'Bullying',
               'Joe Riley', 'South Carolina', 'Jogging')

df <- fuzzylink(dfA, dfB, 
                by = 'name',
                blocking.variables = 'state',
                record_type = 'person')
df

#>                A                         B       sim block        jw match
#> 1      Joe Biden    Joseph Robinette Biden 0.7660565     1 0.7673401   Yes
#> 2   Barack Obama      Barack Hussein Obama 0.8457001     3 0.9200000   Yes
#> 3 George W. Bush        George Walker Bush 0.8447794     4 0.9301587   Yes
#> 4   Bill Clinton William Jefferson Clinton 0.8732311     5 0.5788889   Yes
#> 5   Donald Trump                      <NA>        NA    NA        NA  <NA>
#>   match_probability    state age      hobby
#> 1                 1 Delaware  81   Football
#> 2                 1 Illinois  62 Basketball
#> 3                 1    Texas  77    Reading
#> 4                 1 Arkansas  77  Saxophone
#> 5                NA New York  77       <NA>

Note that because Donald Trump is listed under two different states—New York in dfA and Florida in dfB–the fuzzylink() function no longer returns a match for this record; all blocking variables must match exactly before the function will link two records together. You can specify as many blocking variables as needed by inputting their column names as a vector.

The function returns a few additional columns along with the merged dataframe. The column match_probability reports the model’s estimated probability that the pair of records refer to the same entity. This column should be used to aid in validation and can be used for computing weighted averages if a record in dfA is matched to multiple records in dFB. The columns sim and jw are string distance measures that the model uses to predict whether two records are a match. And if you included blocking.variables in the function call, there will be a column called block with an ID variable denoting which block the records belong to.

A Note On Cost

Because the fuzzylink() function makes several calls to the OpenAI API—which charges a per-token fee—there is a monetary cost associated with each use. Based on the package defaults and API pricing as of August 2025, here is a table of approximate costs for merging datasets of various sizes.

Note that cost scales more quickly with the size of dfA than with dfB, because it is more costly to complete LLM prompts for validation than it is to retrieve embeddings. With particularly large datasets, one can reduce costs by using GPT-3.5 (model = 'gpt-3.5-turbo-instruct'), blocking (blocking.variables), or reducing the maximum number of pairs labeled by the LLM (max_labels).