Cross-correlation (time-lag-correlation) with pandas?

As far as I can tell, there isn't a built in method that does exactly what you are asking. But if you look at the source code for the pandas Series method autocorr, you can see you've got the right idea:

def autocorr(self, lag=1):    """    Lag-N autocorrelation    Parameters    ----------    lag : int, default 1        Number of lags to apply before performing autocorrelation.    Returns    -------    autocorr : float    """    return self.corr(self.shift(lag))

So a simple timelagged cross covariance function would be

def crosscorr(datax, datay, lag=0):    """ Lag-N cross correlation.     Parameters    ----------    lag : int, default 0    datax, datay : pandas.Series objects of equal length    Returns    ----------    crosscorr : float    """    return datax.corr(datay.shift(lag))

Then if you wanted to look at the cross correlations at each month, you could do

 xcov_monthly = [crosscorr(datax, datay, lag=i) for i in range(12)]

There is a better approach: You can create a function that shifted your dataframe first before calling the corr().

Get this dataframe like an example:

d = {'prcp': [0.1,0.2,0.3,0.0], 'stp': [0.0,0.1,0.2,0.3]}df = pd.DataFrame(data=d)>>> df   prcp  stp0   0.1  0.01   0.2  0.12   0.3  0.23   0.0  0.3

Your function to shift others columns (except the target):

def df_shifted(df, target=None, lag=0):    if not lag and not target:        return df           new = {}    for c in df.columns:        if c == target:            new[c] = df[target]        else:            new[c] = df[c].shift(periods=lag)    return  pd.DataFrame(data=new)

Supposing that your target is comparing the prcp (precipitation variable) with stp(atmospheric pressure)

If you do at the present will be:

>>> df.corr()      prcp  stpprcp   1.0 -0.2stp   -0.2  1.0

But if you shifted 1(one) period all other columns and keep the target (prcp):

df_new = df_shifted(df, 'prcp', lag=-1)>>> print df_new   prcp  stp0   0.1  0.11   0.2  0.22   0.3  0.33   0.0  NaN

Note that now the column stp is shift one up position at period, so if you call the corr(), will be:

>>> df_new.corr()      prcp  stpprcp   1.0  1.0stp    1.0  1.0

So, you can do with lag -1, -2, -n!!

To build up on Andre's answer - if you only care about (lagged) correlation to the target, but want to test various lags (e.g. to see which lag gives the highest correlations), you can do something like this:

lagged_correlation = pd.DataFrame.from_dict(    {x: [df[target].corr(df[x].shift(-t)) for t in range(max_lag)] for x in df.columns})

This way, each row corresponds to a different lag value, and each column corresponds to a different variable (one of them is the target itself, giving the autocorrelation).