A quick tutorial on Miller
Recently I had to perform some analyses on a CSV file with a fairly
complex format. I started with
datamash, but I ended up using
miller, because it performed considerably better on the input file I
had, which had a tricky syntax.
This page reports on the tasks I performed and is a quick tutorial of Miller.
The input file
The input file has fields protected by double quotes, numbers with commas as decimal separator (Italian locale), and “-” in place of zeroes. A sample is available here and following table shows its content, formatted by Org Mode.
These are the tasks I had to perform on the file:
- Pre-process the file to simplify analyses: convert separator in decimal numbers and replace “-” with zeroes
- Compute descriptive statistics of “total”
- Compute average total by major (pivot)
- Transpose row and columns of the pivot table computed at the previous step
- Select surname and total
- Select all records with d1 < 13.0
- Sort record by total
Pre-processing the file
One of the issues with the file is the use of field delimiters and
“,” as decimal places, which causes
datamash to incorrectly parse
We fix the format by:
- replacing “-” with “0.00” using sed
- converting the file to tsv (so that commas will appear only as decimal separators) with miller
- replacing “,” with “.” using sed
sed 's/"-"/"0.00"/g' csv-cli-tools-input.csv | mlr --icsv --otsv cat | sed 's/,/./g' | mlr --itsv --ocsv cat > csv-cli-tools-input-cleaned.csv
Now we are ready to perform the analyses.
Descriptive statistics of total
mlr --icsv --ocsv stats1 -a p0,p25,p50,mean,p75,p100,stddev,var -f total csv-cli-tools-input-cleaned.csv
Average total by major
mlr --icsv --ocsv stats1 -a mean -f total -g major csv-cli-tools-input-cleaned.csv | mlr --icsv --ocsv format-values -f "%.2f"
Note. Org Mode cleans data a bit by removing one zero from the second number.
Select surname and total
mlr --icsv --ocsv cut -f surname,total csv-cli-tools-input-cleaned.csv
Select all records with d1 < 13.0
mlr --icsv --ocsv filter '$d1 < 13' csv-cli-tools-input-cleaned.csv
Sort record by total
mlr --icsv --ocsv sort -nr total csv-cli-tools-input-cleaned.csv