title: ValueError: too many values to unpack (expected 2): pandas
body: <p>I am new to using pandas dataframe, I would appreciate any help. I have a set of dates and cashflows for different loans, loan set with 120 period is followed by another loan set with 120 periods in csv file. in total there are 10 loans with 120 periods and 120 cash flows for each loan. I am trying to apply xnpv function to calculate npv for each loan's cashflows. But Python shows an error</p>
  <blockquote>
  <p>ValueError: too many values to unpack (expected 2).</p>
  </blockquote>
  <p>I can't understand what I am doing wrong.</p>
  <p>Here is my code:</p>
  <pre><code>import pandas as pd
  from scipy import optimize
  def secant_method(tol, f, x0):
      x1 = x0*1.1
      while (abs(x1-x0)/abs(x1) &gt; tol):
          x0, x1 = x1, x1-f(x1)*(x1-x0)/(f(x1)-f(x0))
      return x1
    
  def xnpv(rate,cashflows):
      chron_order = sorted(cashflows, key = lambda x: x[0])
      t0 = chron_order[0][0] 
      return sum([cf/(1+rate)**((t-t0).days/365.0) for (t,cf) in chron_order])
  
  s=pd.Series(list(zip(df['date'], df['Total CF'])), index =df.index)
  df1=s.groupby(df['loan_number']).apply(list).reset_index(name='cashflows')
  cashflows=df1['cashflows']
  cashflows
  
  0     [(7/15/2021, 0.152497472), (8/15/2021, 0.23157...
  1     [(7/15/2021, -1.731640118), (8/15/2021, -1.272...
  2     [(7/15/2021, 0.016080295), (8/15/2021, 0.02423...
  3     [(7/15/2021, 0.0), (8/15/2021, 0.0), (9/15/202...
  4     [(7/15/2021, -3.481797138), (8/15/2021, -2.792...
  5     [(7/15/2021, 0.033370756), (8/15/2021, 0.04979...
  6     [(7/15/2021, -2.439990626), (8/15/2021, -2.090...
  7     [(7/15/2021, -2.661802291), (8/15/2021, -2.280...
  8     [(7/15/2021, 0.0), (8/15/2021, 0.0), (9/15/202...
  9     [(7/15/2021, 0.0), (8/15/2021, 0.0), (9/15/202...
  10    [(7/15/2021, -1.555758792), (8/15/2021, -1.321...
  Name: cashflows, dtype: object
  
  xnpv(0.03, cashflows)
  
  ValueError                                Traceback (most recent call last)
  &lt;ipython-input-81-e191dc20193f&gt; in &lt;module&gt;
  ----&gt; 1 xnpv(0.03, cashflows)
  
   &lt;ipython-input-35-8666e85828f1&gt; in xnpv(rate, cashflows)
   23     chron_order = sorted(cashflows, key = lambda x: x[0])
   24     t0 = chron_order[0][0] #t0 is the date of the first cash flow
   ---&gt; 25     return sum([cf/(1+rate)**((t-t0).days/365.0) for (t,cf) in 
   chron_order])
   26 
   27 def xirr(cashflows,guess=0.1):
  
   &lt;ipython-input-35-8666e85828f1&gt; in &lt;listcomp&gt;(.0)
   23     chron_order = sorted(cashflows, key = lambda x: x[0])
   24     t0 = chron_order[0][0] #t0 is the date of the first cash flow
   ---&gt; 25     return sum([cf/(1+rate)**((t-t0).days/365.0) for (t,cf) in 
   chron_order])
   26 
   27 def xirr(cashflows,guess=0.1):
   ValueError: too many values to unpack (expected 2)
  </code></pre>