熊猫：更新其中一个列缺少数据的行的数据框值

Question

I have a dataframe called firstpart .

I'm trying to update the values in one column ( Key ), but only for rows in which another column ( Zone ) has no data.

I'm using this code, which doesn't work:

firstpart.ix[firstpart.Zone ==np.nan,"Key"] = "newvalue"

Neither does this:

firstpart.ix[firstpart.Zone =="","Key"] = "newvalue"

Using this syntax I'm able to update values in rows for which Zone has another value, but for some reason not if I try to select the rows in which it is blank.

What am I doing wrong?

Answer 1

firstpart.ix[firstpart.Zone.isnull()] = "newvalue"

You can't equate NaN to anything.

In [1]: NaN == NaN
Out[1]: False

You need special methods for that, and this is what .isnull() is about.