Min value in each column of a data frame excluding zeros

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The original dataframe is a table like this:

                        S1_r1_ctrl/     S1_r2_ctrl/     S1_r3_ctrl/ sp|P38646|GRP75_HUMAN   2.960000e-06    5.680000e-06    0.000000e+00 sp|O75694-2|NU155_HUMAN 2.710000e-07    0.000000e+00    2.180000e-07 sp|Q05397-2|FAK1_HUMAN  0.000000e+00    2.380000e-07    7.330000e-06 sp|O60671-2|RAD1_HUMAN  NaN             NaN             NaN 

I am looking for the smallest value in each column of a dataframe greater than zero. I was trying to use this example to answer my question. My code looks like:

df.ne(0).idxmin().to_frame('pos').assign(value=lambda d: df.lookup(d.pos, d.index))

but still I get only zeros and my result looks like this:

            pos                     value  S1_r1_ctrl/ sp|Q05397-2|FAK1_HUMAN  0.0 S1_r2_ctrl/ sp|O75694-2|NU155_HUMAN 0.0 S1_r3_ctrl/ sp|P38646|GRP75_HUMAN   0.0 

instead of this:

            pos                     value S1_r1_ctrl/ sp|O75694-2|NU155_HUMAN 2.710000e-07 S1_r2_ctrl/ sp|Q05397-2|FAK1_HUMAN  2.380000e-07 S1_r3_ctrl/ sp|O75694-2|NU155_HUMAN 2.180000e-07 

I guess there might be a problem in data types but I'm not sure. I assumed ne(0) would ignore zeros but it doesn't so I am confused why. And perhaps there's a more intelligent way to find what I need.



df = pd.DataFrame([[0, 0, 0],                    [0, 10, 0],                    [4, 0, 0],                    [1, 2, 3]],                   columns=['first', 'second', 'third']) 

Using a mask with min(0):

df[df.gt(0)].min(0)  first     1.0 second    2.0 third     3.0 dtype: float64 

As @DSM pointed out, this can also be written:



def chris():     df1[df1.gt(0)].min(0)  def chris2():     df1.where(df1.gt(0)).min(0)  def wen():     a=df1.values.T     a = np.ma.masked_equal(a, 0.0, copy=False)     a.min(1)  def haleemur():     df1.replace(0, np.nan).min() 


from timeit import timeit import matplotlib.pyplot as plt  res = pd.DataFrame(        index=['chris', 'chris2', 'wen', 'haleemur'],        columns=[10, 50, 100, 500, 1000, 5000, 10000, 50000, 100000],        dtype=float )  for f in res.index:      for c in res.columns:         df1 = df.copy()         df1 = pd.concat([df1]*c)         stmt = '{}()'.format(f)         setp = 'from __main__ import df1, {}'.format(f)         res.at[f, c] = timeit(stmt, setp, number=50)  ax = res.div(res.min()).T.plot(loglog=True)  ax.set_xlabel("N");  ax.set_ylabel("time (relative)");  plt.show() 


Min value in each column of a data frame excluding zeros


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