Add column to DataFrame in rpy2

Question

I’m using R in python with rpy2. I have a dataframe with some columns in it and I want to add additional one.

As far as I understand I, in R I would write something like this:

df$new_colname <- cumsum(df$oldcolname)

But how can I translate this to rpy2?

I tried many variations of this:

ipdb> d.rx2('cum_misses') <- ro.r.cumsum(d.rx2('misses'))
*** Newest frame

But always get this:

ipdb> p d.rx2('cum_misses')
rpy2.rinterface.NULL

Asked By: mcsim

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Answer 1

So, I found the answer.

To add a column I have to write following code:

d = ro.r.cbind(d, cum_misses=ro.r.cumsum(d.rx2('misses')))

Answered By: mcsim

Answer 2

To get an equivalent of $ assignment use it directly as a three-argument function. First import the base package:

from rpy2.robjects.packages import importr

base = importr('base')
set_column = getattr(base, '$<-')

Then to acheive the equivalent of:

df$new_colname <- value

Use:

df = set_column(df, 'new_colname', value)

Answered By: krassowski

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