Function vsub

alphapy/variables.py:297–353

r"""Substitute the variable parameters into the expression. This function performs the parameter substitution when applying features to a dataframe. It is a mechanism for the user to override the default values in any given expression when defining a feature, instead of having t

(v, expr)

#

def vsub(v, expr):
    r"""Substitute the variable parameters into the expression.

    This function performs the parameter substitution when
    applying features to a dataframe. It is a mechanism for
    the user to override the default values in any given
    expression when defining a feature, instead of having
    to programmatically call a function with new values.  

    Parameters
    ----------
    v : str
        Variable name.
    expr : str
        The expression for substitution.

    Returns
    -------
    newexpr
        The expression with the new, substituted values.

    """
    # numbers pattern
    npat = '[-+]?[0-9]*\.?[0-9]+'
    nreg = re.compile(npat)
    # find all number locations in variable name
    vnums = nreg.findall(v)
    viter = nreg.finditer(v)
    vlocs = []
    for match in viter:
        vlocs.append(match.span())
    # find all number locations in expression
    # find all non-number locations as well
    elen = len(expr)
    enums = nreg.findall(expr)
    eiter = nreg.finditer(expr)
    elocs = []
    enlocs = []
    index = 0
    for match in eiter:
        eloc = match.span()
        elocs.append(eloc)
        enlocs.append((index, eloc[0]))
        index = eloc[1]
    # build new expression
    newexpr = str()
    for i, enloc in enumerate(enlocs):
        if i < len(vlocs):
            newexpr += expr[enloc[0]:enloc[1]] + v[vlocs[i][0]:vlocs[i][1]]
        else:
            newexpr += expr[enloc[0]:enloc[1]] + expr[elocs[i][0]:elocs[i][1]]
    if elocs:
        estart = elocs[len(elocs)-1][1]
    else:
        estart = 0
    newexpr += expr[estart:elen]
    return newexpr