I recently discovered the tool Miller (https://github.com/johnkerl/miller) and believe it to be a better tool for this job. It does what cn set out to accomplish and so much more. Therefore I am archiving this project and removing the Homebrew tap.
Usage: cn [-d] [-h HEADERFILE] LABEL FILE
A handy little utility to give you the index (1-based) of a label/column name in a header of a CSV. Using the -d flag, only the data under the label/column name is returned.
For example:
$ cat data.csv
a,b,c
1,0,0
0,1,0
0,0,1
$ cn b data.csv
2
$ cn -d b data.csv
0
1
0
You can also use stdin:
$ cat data.csv | cn b -
2
$ cat data.csv | cn -d b -
0
1
0
This works well with other tools, e.g.:
$ cat data2.csv
a,b,c
1,2,3
4,5,6
7,8,9
$ cat data2.csv | cn -d b - | awk -F, '{s+=$1}END{print s}'
15
You can even provide the headers from another file, which works well when you are filtering data (coming in from grep via stdin, for example) and still want to select a column. For example, let's say you have the following data. You want to sum the metric_2 column for all rows with type == 'a':
$ cat data3.csv
type,metric_1,metric_2,metric_3
a,1,2,3
b,4,5,6
a,7,8,9
$ cat data3.csv | grep a | cn -h data3.csv -d metric_2 - | awk -F, '{s+=$1}END{print s}'
10
You can install easily with homebrew:
brew tap jefferickson/cn
brew install cn
Or from source:
go get github.com/jefferickson/cn
go install github.com/jefferickson/cn