cprojl - Linux

Overview

cprojl is a command-line tool for projecting tabular data onto selected columns, creating a new table with the specified columns only. It’s commonly used to extract specific columns from large datasets or to create new tables with a subset of columns.

Syntax

cprojl [options] [file] [column1] [column2] ... [columnN]

Options/Flags

  • -d, –delimiter: Specify the delimiter used in the input file; default is whitespace.
  • -h, –help: Display usage information and exit.
  • -i, –input: Specify the input file; defaults to standard input.
  • -o, –output: Specify the output file; defaults to standard output.
  • -s, –skip: Skip the specified number of lines from the beginning of the input file.
  • –null: Interpret empty fields as null values.

Examples

Simple Projection

Extract the first and third columns from a file named "data.txt":

cprojl data.txt 1 3

Projection with Delimiter

Extract specific columns from a CSV file with a comma delimiter:

cprojl -d ',' data.csv 2 4 6

Complex Projection

Extract multiple columns and skip header lines:

cprojl -s 1 data.txt 2 4 6 8

Projection to File

Project columns and save the output to a file:

cprojl -o projected_data.txt data.txt 1 3

Common Issues

No Output

  • Ensure that the specified input file exists and is readable.
  • Verify that the column numbers are correct and within the bounds of the input data.

Incorrect Output

  • Check the delimiter option (-d) to ensure it matches the input file format.
  • Make sure empty fields are interpreted as null values if desired (–null).

Integration

cprojl can be combined with other commands to create powerful data processing pipelines:

  • Use cut to extract specific fields and pipe the output to cprojl for further projection: 
    cut -d ',' data.csv -f 2,4,6 | cprojl
  • Sort the data before projection to obtain specific columns in a sorted order: 
    sort data.txt | cprojl 1 3

Related Commands

  • cut: Extract specific fields from tabular data.
  • sort: Sort data based on specified criteria.
  • join: Merge multiple tables based on common columns.