from functools import partial
from rpy2.ipython import html
html.html_rdataframe=partial(html.html_rdataframe, table_class="docutils")
dplyr in Python¶
We need 2 things for this:
1- A data frame (using one of R’s demo datasets).
from rpy2.robjects.packages import importr, data
datasets = importr('datasets')
mtcars_env = data(datasets).fetch('mtcars')
mtcars = mtcars_env['mtcars']
In addition to that, and because this tutorial is in a notebook, we initialize HTML rendering for R objects (pretty display of R data frames).
import rpy2.ipython.html
rpy2.ipython.html.init_printing()
2- dplyr
from rpy2.robjects.lib.dplyr import DataFrame
from rpy2.robjects import rl
/opt/hostedtoolcache/Python/3.9.17/x64/lib/python3.9/site-packages/rpy2/robjects/lib/dplyr.py:27: UserWarning: This was designed againt dplyr versions starting with 1.0 but you have 1.1.2
warnings.warn(
With this we have the choice of chaining (D3-style)
dataf = (
DataFrame(mtcars)
.filter(rl('gear>3'))
.mutate(powertoweight=rl('hp*36/wt'))
.group_by(rl('gear'))
.summarize(mean_ptw=rl('mean(powertoweight)'))
)
dataf
| gear | mean_ptw | ||
|---|---|---|---|
| 0 | 1 | 4.0 | 1237.1266499803169 |
| 1 | 2 | 5.0 | 2574.0331639315027 |
or with pipes (magrittr style).
# currently no longer working
from rpy2.robjects.lib.dplyr import (filter,
mutate,
group_by,
summarize)
if False:
dataf = (DataFrame(mtcars) >>
filter(rl('gear>3')) >>
mutate(powertoweight=rl('hp*36/wt')) >>
group_by(rl('gear')) >>
summarize(mean_ptw=rl('mean(powertoweight)')))
dataf
The function rl creates unevaluated R language objects, which are
then consummed by the dplyr function, just like it would be
happening when using dplyr in R itself. This means that when writing
mean(powertoweight) the R function mean() is used.
Using a Python function is not too difficult though. We can just call
Python back from R. To achieve this we simply use the decorator
rternalize.
# Define a python function, and make
# it a function R can use through `rternalize`
from rpy2.rinterface import rternalize
@rternalize(signature=False)
def mean_np(x):
import statistics
return statistics.mean(x)
# Bind that function to a symbol in R's
# global environment
from rpy2.robjects import globalenv
globalenv['mean_np'] = mean_np
# Write a dplyr chain of operations,
# using our Python function `mean_np`
dataf = (
DataFrame(mtcars)
.filter(rl('gear>3'))
.mutate(powertoweight=rl('hp*36/wt'))
.group_by(rl('gear'))
.summarize(mean_ptw=rl('mean(powertoweight)'),
mean_np_ptw=rl('mean_np(powertoweight)'))
)
dataf
| gear | mean_ptw | mean_np_ptw | ||
|---|---|---|---|---|
| 0 | 1 | 4.0 | 1237.1266499803169 | 1237.1266499803169 |
| 1 | 2 | 5.0 | 2574.0331639315027 | 2574.0331639315027 |
It is also possible to carry this out without having to place the custom function in R’s global environment, although this is not straightforward.
# First we delete our Python callback in globalenv to
# ensure that we are picking up our callback in our
# specific environment rather than this one.
del(globalenv['mean_np'])
from rpy2.robjects import Environment
my_env = Environment()
my_env['mean_np'] = mean_np
# Create an rlang "quosure" object within
# a given environment. We use the R package
# rlang used by dplyr.
from rpy2.robjects.lib.dplyr import rlang
myquo = rlang.quo.rcall(
[(None, rl('mean_np(rlang::enexpr(powertoweight))'))],
environment=my_env
)
dataf = (
DataFrame(mtcars)
.filter(rl('gear>3'))
.mutate(powertoweight=rl('hp*36/wt'))
.group_by(rl('gear'))
.summarize(
mean_ptw=rl('mean(powertoweight)'),
mean_np_ptw=myquo)
)
dataf
| gear | mean_ptw | mean_np_ptw | ||
|---|---|---|---|---|
| 0 | 1 | 4.0 | 1237.1266499803169 | 1237.1266499803169 |
| 1 | 2 | 5.0 | 2574.0331639315027 | 2574.0331639315027 |
note: rpy2’s interface to dplyr is implementing a fix to the (non-?)issue 1323 (https://github.com/hadley/dplyr/issues/1323)
The seamless translation of transformations to SQL whenever the data are
in a table can be used directly. Since we are lifting the original
implementation of dplyr, it just works.
from rpy2.robjects.lib.dplyr import dplyr
# in-memory SQLite database broken in dplyr's src_sqlite
# db = dplyr.src_sqlite(":memory:")
import tempfile
with tempfile.NamedTemporaryFile() as db_fh:
db = dplyr.src_sqlite(db_fh.name)
# copy the table to that database
dataf_db = DataFrame(mtcars).copy_to(db, name="mtcars")
res = (dataf_db
.filter(rl('gear>3'))
.mutate(powertoweight=rl('hp*36/wt'))
.group_by(rl('gear'))
.summarize(mean_ptw=rl('mean(powertoweight)')))
print(res)
#
# Source: SQL [2 x 2]
# Database: sqlite 3.41.2 [/tmp/tmpxo4an2ls]
gear mean_ptw
<dbl> <dbl>
1 4 1237.
2 5 2574.
Since we are manipulating R objects, anything available to R is also available to us. If we want to see the SQL code generated that’s:
silent = dplyr.show_query(res)
<SQL> SELECT gear, AVG(powertoweight) AS mean_ptw FROM ( SELECT *, (hp * 36.0) / wt AS powertoweight FROM mtcars WHERE (gear > 3.0) ) GROUP BY gear
The conversion rules in rpy2 make the above easily applicable to pandas data frames, completing the “lexical loan” of the dplyr vocabulary from R.
from rpy2.robjects import pandas2ri
from rpy2.robjects import default_converter
# Using a conversion context in which the pandas conversion is
# added to the default conversion rules, the rpy2 object
# `mtcars` (an R data frame) is converted to a pandas data frame.
with (default_converter + pandas2ri.converter).context() as cv:
pd_mtcars = mtcars_env['mtcars']
print(type(pd_mtcars))
<class 'pandas.core.frame.DataFrame'>
Using a local conversion context lets us also go from the pandas data frame to our dplyr-augmented R data frame and use the dplyr transformations on it.
with (default_converter + pandas2ri.converter).context() as cv:
dataf = (DataFrame(pd_mtcars)
.filter(rl('gear>=3'))
.mutate(powertoweight=rl('hp*36/wt'))
.group_by(rl('gear'))
.summarize(mean_ptw=rl('mean(powertoweight)')))
dataf
| mean_ptw | ||
|---|---|---|
| 0 | 1 | 1632.0477884748632 |
Reuse. Get things done. Don’t reimplement.