Apple's iTunes provides a variety of options for organizing, cataloguing and categorizing your music. Specifically, iTunes automatically saves information embedded in songs when you buy or import them and lets you add extra information. Using the extra information fields, such as the grouping fields, helps you further organize your music.
Song Information Overview
ITunes keeps information for each song in your library, including the artist name, album name, date added and any other information included in the song file. Access this information through the "Get Info" window, accessible through the "File" menu. The "Get Info" window for songs also lets you add any information you want, including the year, BPMs, composer, genre, comments and grouping.
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The grouping option allows you to assign your own groups and categories to your music, which can be particularly useful if you have a large music collection with thousands of titles. ITunes does not automatically fill out groupings, which means they are entirely up to you. Use groupings to distinguish between types of music in the same genre. For example, songs within the genre "Rock" could have groupings of "Classic Rock" and "Hard Rock."
To create your own groupings and add them to songs, click a song to highlight it and then click "File" and "Get Info" in the top menu bar. Access the "Get Info" window for an individual song or multiple songs. Type the name for your grouping into the "Grouping" field. Click "OK" to save your changes. Once you add a grouping, iTunes will autosuggest that grouping the next time you begin typing it into a song's information. This helps you keep exactly the same name for your groupings.
Aside from using groupings to organize your music, use them to create customized Smart Playlists. Using the previous example, say you want to create a Smart Playlist of your most-listened-to rock songs, but you specifically want it to contain hard rock. Select "File" and then "New Smart Playlist" from the top menu bar. When the playlist window pops up, click the tab under "Match the Following Rule" and select "Grouping." Click the second tab and select "Is," and then type "Hard Rock" into the field. Click the tab next to "Selected By" and then click "Most Often Played." This will create a playlist specifically containing your hard rock songs, within your rock genre, that have the highest play count.