I have CSV files with numeric data and I would like to perform analysis on this data. I am hoping that using APL will give me more flexibility than reading this into mysql and performing selects. But to start with I would like to do simple extractions like 'select * from mydata where col1 = 2020'. So far I understand I can use Compress. But for that I need to know the expression that would yield the boolean array for the left argument of compress (i.e. the APL version of 'where col1 = 2020'). Online searches did not get me anywhere in that department.
1 Answers
You are indeed right in your speculations.
"col1 = 2020" would be mydata[;1] = 2020 so the entire thing is (mydata[;1] = 2020) ⌿ mydata
My father liked to define
∇ data ← data where condition
data ← condition⌿data
∇
so he could write things like data where data[;1] = 2020
Utilising Dyalog APL features
Dyalog APL provides some notational niceties:
- The inline expression can be written as
mydata ⌿⍨ mydata[;1] = 2020 - The above definition of
wherecan be written simply aswhere ← ⌿⍨
Related