Method and Masking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 10.12 The query() Method (Experimental) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 10.13 (GH4565, GH6998) • Local variable usage has changed in pandas.eval()/DataFrame.eval()/DataFrame.query() (GH5987). For the DataFrame methods, two things have changed – Column names are now given precedence not a column you must still refer to it with the ’@’ prefix. – You can have an expression like df.query(’@a < a’) with no complaints from pandas about am- biguity of the name a. – The top-level pandas

timezone information would be dropped (GH19995, GH27992) • Compatibility with Python 3.8 in DataFrame.query() (GH27261) • Fix to ensure that tab-completion in an IPython console does not raise warnings for 2.2.2 Visualization openpyxl 2.4.8 Reading / writing for xlsx files pandas-gbq 0.8.0 Google Big Query access psycopg2 PostgreSQL engine for sqlalchemy pyarrow 0.9.0 Parquet and feather reading / writing formula.api as sm In [139]: bb = pd.read_csv('data/baseball.csv', index_col='id') In [140]: (bb.query('h > 0') .....: .assign(ln_h=lambda df: np.log(df.h)) .....: .pipe((sm.ols, 'data'), 'hr ~ ln_h

Method and Masking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352 12.13 The query() Method (Experimental) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355 12.14 parameter to read_sql function. Specifying this argument will return an iterator through chunks of the query result (GH2908). • Added support for writing datetime.date and datetime.time object columns with (GH7277) • Bug in Index.delete does not preserve name and freq attributes (GH7302) • Bug in DataFrame.query()/eval where local string variables with the @ sign were being treated as temporaries attempting to

Method and Masking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 12.13 The query() Method (Experimental) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 12.14 parameter to read_sql function. Specifying this argument will return an iterator through chunks of the query result (GH2908). • Added support for writing datetime.date and datetime.time object columns with (GH7277) • Bug in Index.delete does not preserve name and freq attributes (GH7302) • Bug in DataFrame.query()/eval where local string variables with the @ sign were being treated as temporaries attempting to

Method and Masking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427 13.13 The query() Method (Experimental) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430 13.14 pd.read_csv('data/baseball.csv', index_col='id') # sm.poisson takes (formula, data) In [3]: (bb.query('h > 0') ...: .assign(ln_h = lambda df: np.log(df.h)) ...: .pipe((sm.poisson, 'data'), 'hr ~ ln_h DataFrame to just those with a Sepal Length greater than 5, calculate the ratio, and plot In [5]: (iris.query('SepalLength > 5') ...: .assign(SepalRatio = lambda x: x.SepalWidth / x.SepalLength, ...: PetalRatio

Method and Masking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 10.12 The query() Method (Experimental) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 10.13 type Float64Index, and other Indexing enhancements • HDFStore has a new string based syntax for query specification • support for new methods of interpolation • updated timedelta operations • a new for Offsets • isin for DataFrames Several experimental features are added, including: • new eval/query methods for expression evaluation • support for msgpack serialization • an i/o interface to Google’s

. . . . . . . . . . . 547 13.14 The query() Method (Experimental) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550 13.14.1 MultiIndex query() Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553 13.14.2 query() Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554 13.14.3 query() Python versus pandas Syntax Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 559 13.14.7 Performance of query() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560 13.15 Duplicate Data

. . . . . . . . . . . 608 12.15 The query() Method (Experimental) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611 12.15.1 MultiIndex query() Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 614 12.15.2 query() Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615 12.15.3 query() Python versus pandas Syntax Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 620 12.15.7 Performance of query() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621 12.16 Duplicate Data

. . . . . . . . . . . 606 12.15 The query() Method (Experimental) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609 12.15.1 MultiIndex query() Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 612 12.15.2 query() Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613 12.15.3 query() Python versus pandas Syntax Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 618 12.15.7 Performance of query() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 619 12.16 Duplicate Data

. . . . . . . . . . . 545 13.14 The query() Method (Experimental) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 548 13.14.1 MultiIndex query() Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551 13.14.2 query() Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552 13.14.3 query() Python versus pandas Syntax Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 557 13.14.7 Performance of query() . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 558 13.15 Duplicate Data