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November 24, 2018 06:43
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Manipulating dictionary list with SQLite back-end
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from astropy.io.ascii import read | |
selected = ["origin", "dep_delay", "distance"] | |
csv = read("Downloads/nycflights.csv", format = 'csv', data_end = 11)[selected] | |
lst = map(lambda x: dict(zip(x.colnames, x)), csv) | |
from dataset import connect | |
### CREATE IN-MEMORY SQLITE DB ### | |
db = connect('sqlite:///:memory:', row_type = dict) | |
tbl = db.create_table("tbl", primary_id = False) | |
tbl.insert_many(lst) | |
list(db.query("select * from tbl limit 3")) | |
# [{u'dep_delay': 2, u'distance': 1400, u'origin': u'EWR'}, | |
# {u'dep_delay': 4, u'distance': 1416, u'origin': u'LGA'}, | |
# {u'dep_delay': 2, u'distance': 1089, u'origin': u'JFK'}] | |
sum1 = db.create_table("sum1", primary_id = False) | |
from numpy import nanmedian | |
sum1.insert_many( | |
map(lambda x: dict(origin = x, | |
med_dist = nanmedian([i["distance"] for i in | |
db.query("select distance from tbl where origin = :origin", {"origin": x})])), | |
[i["origin"] for i in db.query("select distinct origin from tbl")])) | |
sum2 = db.create_table("sum2", primary_id = False) | |
sum2.insert_many(list(db.query("select origin, ROUND(AVG(dep_delay), 2) as avg_delay from tbl group by origin"))) | |
list(db.query("select a.*, b.avg_delay from sum1 as a, sum2 as b where a.origin = b.origin")) | |
#[{u'avg_delay': -2.33, u'med_dist': 1065.0, u'origin': u'EWR'}, | |
# {u'avg_delay': -1.75, u'med_dist': 747.5, u'origin': u'LGA'}, | |
# {u'avg_delay': -0.67, u'med_dist': 1089.0, u'origin': u'JFK'}] |
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