Summary

This dataset (ml-20m) describes 5-star rating and free-text tagging activity from MovieLens, a movie recommendation service. It contains 20000263 ratings and 465564 tag applications across 27278 movies. These data were created by 138493 users between January 09, 1995 and March 31, 2015. This dataset was generated on October 17, 2016.

Users were selected at random for inclusion. All selected users had rated at least 20 movies. No demographic information is included. Each user is represented by an id, and no other information is provided.

The data are contained in six files, genome-scores.csv, genome-tags.csv, links.csv, movies.csv, ratings.csv and tags.csv. More details about the contents and use of all these files follows.

Content and Use of Files

Verifying the Dataset Contents

We encourage you to verify that the dataset you have on your computer is identical to the ones hosted at grouplens.org. This is an important step if you downloaded the dataset from a location other than grouplens.org, or if you wish to publish research results based on analysis of the MovieLens dataset.

We provide a MD5 checksum with the same name as the downloadable .zip file, but with a .md5 file extension. To verify the dataset:

# on linux
md5sum ml-20m.zip; cat ml-20m.zip.md5

# on OSX
md5 ml-20m.zip; cat ml-20m.zip.md5

# windows users can download a tool from Microsoft (or elsewhere) that verifies MD5 checksums

Check that the two lines of output contain the same hash value.

Formatting and Encoding

The dataset files are written as comma-separated values files with a single header row. Columns that contain commas (,) are escaped using double-quotes ("). These files are encoded as UTF-8. If accented characters in movie titles or tag values (e.g. Misérables, Les (1995)) display incorrectly, make sure that any program reading the data, such as a text editor, terminal, or script, is configured for UTF-8.

User Ids

MovieLens users were selected at random for inclusion. Their ids have been anonymized. User ids are consistent between ratings.csv and tags.csv (i.e., the same id refers to the same user across the two files).

Movie Ids

Only movies with at least one rating or tag are included in the dataset. These movie ids are consistent with those used on the MovieLens web site (e.g., id 1 corresponds to the URL https://movielens.org/movies/1). Movie ids are consistent between ratings.csv, tags.csv, movies.csv, and links.csv (i.e., the same id refers to the same movie across these four data files).

Ratings Data File Structure (ratings.csv)

All ratings are contained in the file ratings.csv. Each line of this file after the header row represents one rating of one movie by one user, and has the following format:

userId,movieId,rating,timestamp

The lines within this file are ordered first by userId, then, within user, by movieId.

Ratings are made on a 5-star scale, with half-star increments (0.5 stars - 5.0 stars).

Timestamps represent seconds since midnight Coordinated Universal Time (UTC) of January 1, 1970.

Tags Data File Structure (tags.csv)

All tags are contained in the file tags.csv. Each line of this file after the header row represents one tag applied to one movie by one user, and has the following format:

userId,movieId,tag,timestamp

The lines within this file are ordered first by userId, then, within user, by movieId.

Tags are user-generated metadata about movies. Each tag is typically a single word or short phrase. The meaning, value, and purpose of a particular tag is determined by each user.

Timestamps represent seconds since midnight Coordinated Universal Time (UTC) of January 1, 1970.

Movies Data File Structure (movies.csv)

Movie information is contained in the file movies.csv. Each line of this file after the header row represents one movie, and has the following format:

movieId,title,genres

Movie titles are entered manually or imported from https://www.themoviedb.org/, and include the year of release in parentheses. Errors and inconsistencies may exist in these titles.

Genres are a pipe-separated list, and are selected from the following:

• Action

• Adventure

• Animation

• Children's

• Comedy

• Crime

• Documentary

• Drama

• Fantasy

• Film-Noir

• Horror

• Musical

• Mystery

• Romance

• Sci-Fi

• Thriller

• War

• Western

• (no genres listed)

Links Data File Structure (links.csv)

Identifiers that can be used to link to other sources of movie data are contained in the file links.csv. Each line of this file after the header row represents one movie, and has the following format:

movieId,imdbId,tmdbId

movieId is an identifier for movies used by https://movielens.org. E.g., the movie Toy Story has the link https://movielens.org/movies/1.

imdbId is an identifier for movies used by http://www.imdb.com. E.g., the movie Toy Story has the link http://www.imdb.com/title/tt0114709/.

tmdbId is an identifier for movies used by https://www.themoviedb.org. E.g., the movie Toy Story has the link https://www.themoviedb.org/movie/862.

Use of the resources listed above is subject to the terms of each provider.

Tag Genome (genome-scores.csv and genome-tags.csv)

This data set includes a current copy of the Tag Genome.

The tag genome is a data structure that contains tag relevance scores for movies. The structure is a dense matrix: each movie in the genome has a value for every tag in the genome.

As described in this article, the tag genome encodes how strongly movies exhibit particular properties represented by tags (atmospheric, thought-provoking, realistic, etc.). The tag genome was computed using a machine learning algorithm on user-contributed content including tags, ratings, and textual reviews.

The genome is split into two files. The file genome-scores.csv contains movie-tag relevance data in the following format:

movieId,tagId,relevance

The second file, genome-tags.csv, provides the tag descriptions for the tag IDs in the genome file, in the following format:

tagId,tag

The tagId values are generated when the data set is exported, so they may vary from version to version of the MovieLens data sets.

Cross-Validation

Prior versions of the MovieLens dataset included either pre-computed cross-folds or scripts to perform this computation. We no longer bundle either of these features with the dataset, since most modern toolkits provide this as a built-in feature. If you wish to learn about standard approaches to cross-fold computation in the context of recommender systems evaluation, see LensKit for tools, documentation, and open-source code examples.