A python package that allows you to execute NoSQL-style queries on CSV files.
Project description
CSV Query
A python package that allows you to execute NoSQL-style queries on CSV files.
Downloading
pip install csvquery
Usage
Loading data
Use open_csv(path) to produce a Dataset from a CSV file:
from csvquery import open_csv
dataset = open_csv("path/to/file.csv")
Indexing
Once you have a dataset, use Dataset.index(column_name[, comparison_operation]) to sort the rows of data based on the values in a specified column. Sorting the data is optional, but doing so allows you to do binary searches which have a time complexity of just O(log(n)).
from csvquery import open_csv
dataset = open_csv("people.csv")
dataset.index("age") # sorts people by ascending age
The default comparison operation used to sort the data is a float comparison. You can import the csvquery.Comparisons class to use other common comparison operations:
from csvquery import open_csv, Comparisons
dataset = open_csv("people.csv")
dataset.index("name", Comparisons.strings)
Comparisons.integers >> lambda a, b: int(a) < int(b)
Comparisons.floats >> lambda a, b: float(a) < float(b)
Comparisons.strings >> lambda a, b: a < b
The csvquery.Comparisons class also has a static method called get_date_comparison(format_string) which returns a custom date comparison function (based on the specified format) that you can pass as the comparison operation:
from csvquery import open_csv, Comparisons
dataset = open_csv("people.csv")
data.index("date_of_birth", Comparisons.get_date_comparison("YYYY-MM-DD"))
You can also specify your own custom comparison operation:
from csvquery import open_csv
dataset = open_csv("people.csv")
dataset.index("name", lambda a, b: a**2 < b**2)
Queries
Use Dataset.query(filter_object) to fetch rows of data that pass through specified filters:
from csvquery import open_csv
dataset = open_csv("people.csv")
dataset.index("age")
voter_dataset = dataset.query({
"age": { # this filter will run as a binary search since we indexed the data by age
"gte": 18 # the query will only return people who's age is greater than or equal to 18
},
"citizenship" { # this will run after the binary search to filter the narrowed-down data
"eq": "USA" # people will only pass this filter if their "citizenship" field is equal to "USA"
}
})
Since Dataset.query(filter_object) returns another Dataset, you can query the resulting dataset as well:
voters_named_john = voter_dataset.query({
"name": {
"eq": "John"
}
})
You can also use the csvquery.Operators class instead of operator strings:
from csvquery import Operators
voters_named_john = voter_dataset.query({
"name": {
Operators.equal : "John"
}
})
The general structure of a filter_object is as follows:
{
"column_name_1": {
Operators.a: "value_1",
Operators.b: "value_2",
...
Operators.x: "value_x"
},
"column_name_2": {
...
},
...
"column_name_x": {
...
}
}
Valid operators
- eq: equals (cannot be combined with any other operator, including itself)
- neq: not equal
- lt: less than
- gt: greater than
- lte: less than or equal
- gte: greater than or equal
NOTE: If you want to use a comparison operator like gt or lte on a column that was not indexed, you need to provide a comparison operator in the filter_object like so:
from csvquery import open_csv, Operations, Comparisons
dataset = open_csv("people.csv")
dataset.index("citizenship") # sorts people by citizenship
voter_dataset = dataset.query({
"citizenship": { # binary search
Operations.equal: "USA"
},
"age" { # not a binary search
Operations.greater_than_or_equal: "18"
Operations.comparison: Comparisons.integers
}
})
Outputting data
Use Dataset.print_data([column_names]) to output your new data to the console:
voter_dataset.print_data()
You can optionally specify which columns to print:
voter_dataset.print_data(["name", "age"])
You can also save Dataset objects as CSV files using Dataset.save_csv(filepath[, delimiter[, columns])
voter_dataset.save_csv("output.csv", ";", ["name", "age"])
To access the data as a two-dimensional array, just use the data attribute of the Dataset object:
for row in voter_dataset.data:
print(row[0])
...
More examples
SQL translation
SQL query
SELECT name, age FROM people
WHERE age >= 18 AND citizenship = "USA";
Python NoSQL query
voters = people.query({
"age": {
"gte": 18
},
"citizenship": "USA"
})
voters.print_data(["name", "age"])
Printing certain columns
dataset = open_csv("people.csv")
dataset.print_data(dataset.column_names[2:5])
Rewriting a CSV file with fewer columns and a different delimiter
dataset = open_csv("people.csv")
dataset.save_csv("people.csv", ";", dataset.column_names[2:5])
The "eq" operator is optional
dataset = csvquery.open_csv("people.csv")
dataset.query({
"name":"John"
})
Chaining
(
open_csv("people.csv")
.index("age")
.query({"age":{"gte":18}, "citizenship":"USA"})
.print_data(["name", "id"])
.save_csv("voters.csv", ",", ["name", "id"])
)
Already sorted csv
people = open_csv("people_sorted_by_age.csv")
people.already_indexed("age", Comparisons.integer) # this allows you to do binary searches
babies = people.query({"age": 0}).print_data(["name"])
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