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head

Overview

kgtk head is analogous to the POSIX 'head' command. It takes optional input and output files, and a primary option, -n N.

When -n N is positive, it will pass just the first N data edges of a KGTK input file to the KGTK output file.

When -n N is negative, it will pass all except the last N edges of the KGTK input file to the KGTK output file.

The header record, cotaining the column names, is always passed and is not included in the edge limit, N.

Multiplier suffixes are not supported.

This command defaults to --mode=NONE since it doesn't attach special meaning to particular columns.

Although a positive -n N has the same effect as KgtkReader's record_limit option, this code currently implements the limit itself.

Usage

usage: kgtk head [-h] [-i INPUT_FILE] [-o OUTPUT_FILE] [-n EDGE_LIMIT]
                 [-v [optional True|False]]

This utility is analogous to the POSIX "head" command. 

When "-n N" is positive, it will pass just the first N data edges of a KGTK input file to the KGTK output file. 

When "-n N" is negative, it will pass all except the last N edges of the KGTK input file to the KGTK output file. 

The header record, cotaining the column names, is always passed and is not included in N. 

Multiplier suffixes are not supported. 

Use this command to filter the output of any KGTK command: 

kgtk xxx / head -n 20 

Use it to limit the records in a file: 

kgtk head -i file.tsv -o file.html

This command defaults to --mode=NONE so it will work with TSV files that do not follow KGTK column naming conventions.

Additional options are shown in expert help.
kgtk --expert html --help

optional arguments:
  -h, --help            show this help message and exit
  -i INPUT_FILE, --input-file INPUT_FILE
                        The KGTK input file. (May be omitted or '-' for
                        stdin.)
  -o OUTPUT_FILE, --output-file OUTPUT_FILE
                        The KGTK output file. (May be omitted or '-' for
                        stdout.)
  -n EDGE_LIMIT, --edges EDGE_LIMIT
                        The number of records to pass if positive
                        (default=10).

  -v [optional True|False], --verbose [optional True|False]
                        Print additional progress messages (default=False).

Examples

See the First 10 Edges

Using the default value for -n N:

kgtk head -i examples/docs/head-example1.tsv
node1 label node2 id
red property True
red isa rgbcolor
red maxoccurs 1
green property True
green isa rgbcolor
green maxoccurs 1
blue property True
blue isa rgbcolor
blue maxoccurs 1
rgbcolor datatype True

See the First 15 Edges

kgtk head -n 15 -i examples/docs/head-example1.tsv
node1 label node2 id
red property True
red isa rgbcolor
red maxoccurs 1
green property True
green isa rgbcolor
green maxoccurs 1
blue property True
blue isa rgbcolor
blue maxoccurs 1
rgbcolor datatype True
rgbcolor node1_type symbol
rgbcolor node2_type number
rgbcolor minval 0.0
rgbcolor maxval 1.0
rgbcolor requires red

See All Except the Last 20 Edges

kgtk head -n -20 -i examples/docs/head-example1.tsv
node1 label node2 id
red property True
red isa rgbcolor
red maxoccurs 1
green property True
green isa rgbcolor
green maxoccurs 1
blue property True
blue isa rgbcolor
blue maxoccurs 1
rgbcolor datatype True
rgbcolor node1_type symbol
rgbcolor node2_type number
rgbcolor minval 0.0
rgbcolor maxval 1.0
rgbcolor requires red
rgbcolor requires green
rgbcolor requires blue
rgbcolor isa colorclass
rgbcolor prohibits colorname
colorname property True
colorname isa colorclass
colorname node1_type symbol
colorname node2_type symbol
colorname node2_values red
colorname node2_values green
colorname node2_values blue
colorname node2_values yellow

See the Complete File

Using a very large number, we can use kgtk head to display the entire file.

kgtk head -n 999999999 -i examples/docs/head-example1.tsv
node1 label node2 id
red property True
red isa rgbcolor
red maxoccurs 1
green property True
green isa rgbcolor
green maxoccurs 1
blue property True
blue isa rgbcolor
blue maxoccurs 1
rgbcolor datatype True
rgbcolor node1_type symbol
rgbcolor node2_type number
rgbcolor minval 0.0
rgbcolor maxval 1.0
rgbcolor requires red
rgbcolor requires green
rgbcolor requires blue
rgbcolor isa colorclass
rgbcolor prohibits colorname
colorname property True
colorname isa colorclass
colorname node1_type symbol
colorname node2_type symbol
colorname node2_values red
colorname node2_values green
colorname node2_values blue
colorname node2_values yellow
colorclass mustoccur True
cube property True
cube isa boxshape
cone property True
cone isa pointyshape
cone isa roundshape
sphere property True
sphere isa roundshape
pyramid property True
pyramid isa pointyshape
cylinder property True
cylinder isa roundshape
boxshape datatype True
boxshape isa shape
pointyshape datatype True
pointyshape isa shape
roundshape datatype True
roundshape isa shape
shape datatype True
shape mustoccur True