I am getting an error and I'm not sure how to fix it.
The following seems to work:
def random(row):
return [1,2,3,4]
df = pandas.DataFrame(np.random.randn(5, 4), columns=list('ABCD'))
df.apply(func = random, axis = 1)
and my output is:
[1,2,3,4]
[1,2,3,4]
[1,2,3,4]
[1,2,3,4]
However, when I change one of the of the columns to a value such as 1 or None:
def random(row):
return [1,2,3,4]
df = pandas.DataFrame(np.random.randn(5, 4), columns=list('ABCD'))
df['E'] = 1
df.apply(func = random, axis = 1)
I get the the error:
ValueError: Shape of passed values is (5,), indices imply (5, 5)
I've been wrestling with this for a few days now and nothing seems to work. What is interesting is that when I change
def random(row):
return [1,2,3,4]
to
def random(row):
print [1,2,3,4]
everything seems to work normally.
This question is a clearer way of asking this question, which I feel may have been confusing.
My goal is to compute a list for each row and then create a column out of that.
EDIT: I originally start with a dataframe that hase one column. I add 4 columns in 4 difference apply steps, and then when I try to add another column I get this error.
The shape of a DataFrame is a tuple of array dimensions that tells the number of rows and columns of a given DataFrame.
pandas can represent integer data with possibly missing values using arrays.
If your goal is add new column to DataFrame, just write your function as function returning scalar value (not list), something like this:
>>> def random(row):
... return row.mean()
and then use apply:
>>> df['new'] = df.apply(func = random, axis = 1)
>>> df
A B C D new
0 0.201143 -2.345828 -2.186106 -0.784721 -1.278878
1 -0.198460 0.544879 0.554407 -0.161357 0.184867
2 0.269807 1.132344 0.120303 -0.116843 0.351403
3 -1.131396 1.278477 1.567599 0.483912 0.549648
4 0.288147 0.382764 -0.840972 0.838950 0.167222
I don't know if it possible for your new column to contain lists, but it deinitely possible to contain tuples ((...)
instead of [...]
):
>>> def random(row):
... return (1,2,3,4,5)
...
>>> df['new'] = df.apply(func = random, axis = 1)
>>> df
A B C D new
0 0.201143 -2.345828 -2.186106 -0.784721 (1, 2, 3, 4, 5)
1 -0.198460 0.544879 0.554407 -0.161357 (1, 2, 3, 4, 5)
2 0.269807 1.132344 0.120303 -0.116843 (1, 2, 3, 4, 5)
3 -1.131396 1.278477 1.567599 0.483912 (1, 2, 3, 4, 5)
4 0.288147 0.382764 -0.840972 0.838950 (1, 2, 3, 4, 5)
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