Pandas: How many times does a string appear in a dataframe cell?

Question

I believe to have a simple problem. I have a pandas dataframe df looking quite similar to this:

data = [{"Text" : "Dog", "Dog" : 1},
        {"Text" : "Cat", "Dog" : 0}, 
        {"Text" : "Mouse", "Dog" : 0}, 
        {"Text" : "Dog", "Dog" : 1}]

df = pd.DataFrame(data)

I am trying to search the column Text for a number of keywords and count how many times they appear in each cell. The result is supposed to be stored in a new column that shows how many times the specific keyword was found. The result is supposed to be just like the Dog column.

I tried using pandas str.count. It works just fine. But in the moment I try to store the result in a new column, I run in to trouble:

mykewords = ('Cat', 'Mouse')
df['Cat'] = df.Text.str.count("Cat")

I get the following error message:

A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
  if __name__ == '__main__':

I have two questions:

1. What am I doing wrong and how can I solve it?
2. How can loop through all keywords in mykeywords and get a column each?

Thank you very much for any help in advance!

Answer 1

If possible multiple values in text and need count values:

mykewords = ('Cat', 'Mouse')
for x in mykewords:
    df[x] = df.Text.str.count(x)

Better solution is use words boundaries with Series.str.findall and Series.str.len:

for x in mykewords:
    df[x] = df.Text.str.findall(r"\b{}\b".format(x)).str.len()

Difference in solutions:

data = [{"Text" : "Dog Cat Catman", "Dog" : 1},
        {"Text" : "Cat Cat", "Dog" : 0}, 
        {"Text" : "Mouse Cat", "Dog" : 0}, 
        {"Text" : "Dog", "Dog" : 1}]

df = pd.DataFrame(data)
df1 = df.copy()
print (df)
   Dog            Text
0    1  Dog Cat Catman
1    0         Cat Cat
2    0       Mouse Cat
3    1             Dog

mykewords = ('Cat', 'Mouse')

for x in mykewords:
    df[x] = df.Text.str.findall(r"\b{}\b".format(x)).str.len()
print (df)
   Dog            Text  Cat  Mouse
0    1  Dog Cat Catman    1      0 <-not match Catman
1    0         Cat Cat    2      0
2    0       Mouse Cat    1      1
3    1             Dog    0      0

for x in mykewords:
    df1[x] = df1.Text.str.count(x)
print (df1)
   Dog            Text  Cat  Mouse
0    1  Dog Cat Catman    2      0 <-match Catman
1    0         Cat Cat    2      0
2    0       Mouse Cat    1      1
3    1             Dog    0      0