19.1 CSV Basics

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A verb is required to let mlr know what action to undertake. There are many, but some common verbs include

verb	action
cat	output the supplied input
cut -f name,pid	retain selected columns
filter ‘\(id == "u1234567"'|retain rows that meet some conditions| |put '\)mark = round($total)’	construct new variables
rename ‘Patient ID’,pid	rename variables
sort -f mark	sort rows on a particular field
then	to construct a pipeline

To get the column names for the csv file:

$ mlr cat example.csv | head -1
1=color,2=shape,3=flag,4=index,5=quantity,6=rate

A verb is required to specify an action. Here we simply cat the file:

$ mlr cat example.csv
1=color,2=shape,3=flag,4=index,5=quantity,6=rate
1=yellow,2=triangle,3=1,4=11,5=43.6498,6=9.8870
1=red,2=square,3=1,4=15,5=79.2778,6=0.0130
1=red,2=circle,3=1,4=16,5=13.8103,6=2.9010
1=red,2=square,3=0,4=48,5=77.5542,6=7.4670
1=purple,2=triangle,3=0,4=51,5=81.2290,6=8.5910
1=red,2=square,3=0,4=64,5=77.1991,6=9.5310
1=purple,2=triangle,3=0,4=65,5=80.1405,6=5.8240
1=yellow,2=circle,3=1,4=73,5=63.9785,6=4.2370
1=yellow,2=circle,3=1,4=87,5=63.5058,6=8.3350
1=purple,2=square,3=0,4=91,5=72.3735,6=8.2430

Specify that the input is a csv file using --icsv:

$ mlr --icsv cat example.csv
color=yellow,shape=triangle,flag=1,index=11,quantity=43.6498,rate=9.8870
color=red,shape=square,flag=1,index=15,quantity=79.2778,rate=0.0130
color=red,shape=circle,flag=1,index=16,quantity=13.8103,rate=2.9010
color=red,shape=square,flag=0,index=48,quantity=77.5542,rate=7.4670
color=purple,shape=triangle,flag=0,index=51,quantity=81.2290,rate=8.5910
color=red,shape=square,flag=0,index=64,quantity=77.1991,rate=9.5310
color=purple,shape=triangle,flag=0,index=65,quantity=80.1405,rate=5.8240
color=yellow,shape=circle,flag=1,index=73,quantity=63.9785,rate=4.2370
color=yellow,shape=circle,flag=1,index=87,quantity=63.5058,rate=8.3350
color=purple,shape=square,flag=0,index=91,quantity=72.3735,rate=8.2430

And that both input and output are csv with --csv:

$ mlr --csv cat example.csv
color,shape,flag,index,quantity,rate
yellow,triangle,1,11,43.6498,9.8870
red,square,1,15,79.2778,0.0130
red,circle,1,16,13.8103,2.9010
red,square,0,48,77.5542,7.4670
purple,triangle,0,51,81.2290,8.5910
red,square,0,64,77.1991,9.5310
purple,triangle,0,65,80.1405,5.8240
yellow,circle,1,73,63.9785,4.2370
yellow,circle,1,87,63.5058,8.3350
purple,square,0,91,72.3735,8.2430

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