Syntax for `apply` pandas function in ruby

I need to convert a python script into ruby. I use for that the gems Pandas and Numpy which make the work quite simple.

For example I have these kind of lines:

# python# DF is a dataframe from PandasDF['VAL'].ewm(span = vDAY).mean()DF['VOLAT'].rolling(vDAY).std()

so no question asked, I convert like this:

# rubydf['VAL'].ewm(span: vDAY).meandf['VOLAT'].rolling(vDAY).std

easy.

But I have a function apply from Pandas which takes a function as first argument and I really don't know how to convert it in ruby.It's something like that :

# pythonimport numpy as npDF['VAL'].rolling(vDAY).apply(lambda x: np.polyfit(range(len(x)), x, 1)[0])# output=> NaN or Float

I tried to decomposed the lambda like this:

# rubypolyfit = ->(x) { t = Numpy.polyfit((0...x.size).to_a, x, 1); t[0] }puts polyfit.call(<insert Array argument>) #=> I have a satisfying output for my lambda# but...df['VAL'].rolling(vDAY).apply(&polyfit)# output=> `apply': <class 'TypeError'>: must be real number, not NoneType (PyCall::PyError)# ordf['VAL'].rolling(vDAY).apply{ |x| polyfit.call(x) }# output=> `apply': <class 'TypeError'>: apply() missing 1 required positional argument: 'func' (PyCall::PyError)# ordf['VAL'].rolling(vDAY).apply(polyfit)#output=> `apply': <class 'TypeError'>: must be real number, not NoneType (PyCall::PyError)# ordf['VAL'].rolling(vDAY).apply(:polyfit)# output=> `apply': <class 'TypeError'>: 'str' object is not callable (PyCall::PyError)

It's obviously not working. The problem is this "x" argument in the python inline syntax that I really don't know how to get it "the ruby way"

If someone can "translate" this apply function from python syntax to ruby, it would be really nice :)

I just want to point out that I'm a ruby/rails developer and I don't know python professionally speaking.

UPDATE:

Ok, it's a complete misunderstanding of python code for my part: apply needs a function argument as a callable object. So in ruby it's not a lambda but a Proc I need.

So the solution for those who encounter the same problem:

# rubypolyfit = Proc.new { t = Numpy.polyfit((0...x.size).to_a, x, 1); t[0] }df['VAL'].rolling(vDAY).apply(polyfit)