Trix Indices

A Trix index consists of a pair of files that allow for fast look-up of free text associated with a list of identifiers. The index is created from a single line-oriented text file using the program ixIxx. Each line in the text file starts with an identifier, followed by free text associated with the ID. For a more complete description of how to make a searchable track hub (or custom track), please visit the Quick Start Guide to Searchable track hubs.

To complete the steps below you must first download the ixIxx utility. For more information on downloading our command line utilities, see these instructions.

Example 1

To create a Trix index, follow these steps:

Prepare a text file that associates your IDs with free text:

    id1 this is text for id1
    id2 this is text for id2
    id3 this is text for id3

Run the ixIxx program on your text file.

    ixIxx input.txt myTrix.ix myTrix.ixx

Example 2

If you have a bigBed track with unique gene names such as SIRT1, BRCA1, TP53 in the fourth name column, and you built the bigBed using the option of -extraIndex=name to index the name field you can create an input.txt such as the following that associates the bigBed name with other identifiers people might search for or with shorter spellings of the names:
```
    SIRT1 sirt1 sir sirt SIR SIRT Sirtuin SIR2-Like ENSG00000096717 NM_012238
    BRCA1 brca1 brca brc BRC BRCA breast cancer 1 ENSG00000012048 NM_007300
    TP53 tp53 tp5 TP5 Tumor Protein P53 ENSG00000141510 NM_001126112
```
You would then run the ixIxx program on your text file, taking into account the length of your longest word.
```
    ixIxx input.txt myTrix.ix myTrix.ixx
```

The ixIxx utility has a default of 31 characters for words. If you build an input.txt with longer words, such as very long accessions, you neeed to add the option -maxWordLength=N to override the default and expand it to the size you are using for the longest words in your index.

Resources and examples

If you want to use your Trix index in a track hub, see the searchTrix setting in the Track Database Definition Document.

Review our Quick Start Guide to Searchable track hubs for illustrated steps building a track hub.

There are also tools available for taking genePred format to trix format, such as this gpToIx.pl perl script.