从python中的pandas Series和DataFrames获取字符串？

Question

I have this dataframe in pandas:

d=pandas.DataFrame([{"a": 1, "b": 1}, {"c": 2, "b": 4}])
d["name"] = ["Hello", "World"]

I want to select an element based on its string value in "name" column and then get the value as a string. To select the element:

d[d["name"] == "World"]["name"]
Out:
1    World
Name: name

The problem is that it doesn't give a simple string but a series. Casting to a string won't help -- how can I just get the string "World" out of this? Is this the only way?

d[d["name"] == "World"]["name"].values[0]

thanks.?

Answer 1

There's one method that no one mentioned that might be worth noting. This was a problem I was having where I was doing multiple criteria checks and getting back a single item Series (basically a unique row result). If you have a single item in a Series and just need that item OR know the index of the particular item you want to gather, just do this:

d[d["name"] == "World"].tolist()[0]

for the first (and only) item in a single item Series.

Or this:

d[d["name"] == "World"].tolist()[index]

where index is the index of the item you are looking for in the Series.

If you want it as a string, you may have to cast as a string if it is not already stringified by default.

Answer 2

As @DSM points out, in general there could be many rows with name 'World' , so somewhere down the line we'll need to pick one.

One way to do this which seems kind of nice could be to use where (and then max ):

In [11]: d.name.where(d.name == 'World', np.nan)
Out[11]: 
0      NaN
1    World
Name: name, dtype: object

In [12]: d.name.where(d.name == 'World', np.nan).max()
Out[12]: 'World'

Note: if there is no row with name 'World' this will return NaN.

Answer 3

UPDATE: Not recommended as it truncates long text unless using pandas > 1.0 (not tested)

Not sure what versions of Pandas this works in, but its one other option:

d[d["name"] == "World"].to_string(index=False)

and if more than one row there are other options:

 max_rows      int, optional

Maximum number of rows to show before truncating. If None, show all.

 min_rows      int, optional

The number of rows to display in a truncated repr (when number of rows is above max_rows).