Convert GCT to TXT

A program may require a .txt filename even though a GCT file already contains plain tab-delimited text. Renaming or copying the file lets you edit, share, or import the matrix without changing its data structure.

What the GCT format is

GCT usually means Gene Cluster Text, a tab-delimited format for gene-expression matrices and related genomic tables. Broad Institute GSEA and GenePattern commonly create or read it.

A typical GCT 1.2 file starts with #1.2, followed by a row-and-column count, a header containing identifiers and sample names, and rows containing gene identifiers, descriptions, and values. GCT 1.3 files can contain additional metadata. Standard GCT files are normally uncompressed plain text, although datasets may be distributed as compressed files such as .gct.gz.

What the TXT format is

.txt is a generic filename extension, not a defined data format. A TXT file may contain tab-separated, comma-separated, space-separated, or free-form text; the extension does not specify the delimiter, encoding, headers, or schema.

TXT is useful when receiving software checks for a generic text extension, when inspecting the matrix in Notepad++, VS Code, or another editor, or when sharing data with users who do not have a specialist genomics application. Keep the tabs and GCT header lines if the file must remain usable as a matrix.

How to convert GCT to TXT

For an unchanged copy

1. Back up the original input.gct file.
2. If the source is .gct.gz, decompress it first with a tool such as 7-Zip or gunzip.
3. Rename the file to output.txt in the file manager, or use an exact copy command. Renaming changes only the filename extension.

On macOS or Linux:

cp input.gct output.txt

In Windows PowerShell:

Copy-Item input.gct output.txt

Open the result in a plain-text editor and verify that the version line, dimension line, tab alignment, identifiers, and numeric values are unchanged. Do not use a word processor.

For controlled spreadsheet editing

1. Open LibreOffice Calc and choose File → Open.
2. In the import dialog, select Tab as the separator. Disable automatic type detection where available so identifiers are not converted to dates, scientific notation, or numbers.
3. After editing, choose File → Save As, select a text or CSV/text format, set the field delimiter to a tab, and save as output.txt.
4. Open the saved file in a text editor and check the GCT header, column count, row count, tabs, and identifier values.

Spreadsheet export can change line endings, quoting, encoding, empty cells, numeric precision, or identifier formatting. Use direct copying when GSEA, GenePattern, or another GCT parser must read the file.

Compatibility and online tools

Changing .gct to .txt does not convert the internal structure. A TXT importer may reject the GCT version and dimension lines, while GSEA or GenePattern may require the original GCT extension and exact header structure. A file renamed to TXT is therefore not automatically compatible with every program that accepts text.

Do not replace tabs with spaces, delete metadata rows, reorder columns, or remove the description column unless the receiving application specifies a different schema. Preserve the original GCT because TXT has no standard way to record the delimiter, encoding, or matrix format.

No online converter is normally needed for this operation, and uploading expression data may expose unpublished or sensitive research. General services such as Convertio or Zamzar should be used only if they explicitly accept the source file and the required tab-delimited output; many generic converters do not recognize GCT and may reformat the matrix. A local rename, Notepad++, or VS Code is safer for an exact copy.