Create new column and put conditional value pandas dataframe

Question

I have dataframe :

 sepallength sepalwidth petallength petalwidth        class   cluster
0         5.1        3.5         1.4        0.2  Iris-setosa  cluster1
1         4.9          3         1.4        0.2  Iris-setosa  cluster1
2         4.7        3.2         1.3        0.2  Iris-setosa  cluster1
3         4.6        3.1         1.5        0.2  Iris-setosa  cluster1
4           5        3.6         1.4        0.2  Iris-setosa  cluster1
5         5.4        3.9         1.7        0.4  Iris-setosa  cluster1
6         4.6        3.4         1.4        0.3  Iris-setosa  cluster1
7           5        3.4         1.5        0.2  Iris-setosa  cluster1
8         4.4        2.9         1.4        0.2  Iris-setosa  cluster1
9         4.9        3.1         1.5        0.1  Iris-setosa  cluster1

and a dictionary :

{'cluster2': 'Iris-virginica', 'cluster0': 'Iris-versicolor', 'cluster1': 'Iris-setosa'}

I need to add another column and fill it with values from this dictionary of df['cluster'] == key

I have tried using np.where

def countTruth(df):
    # dictionary mapping cluster to most frequent class

    clustersClass = df.groupby(['cluster'])['class'].agg(lambda x:x.value_counts().index[0]).to_dict()
    for eachKey in clustersClass:
        newv = clustersClass[eachKey]
        print df
        df['new'] = np.where(df['cluster']==eachKey , newv)

crashes saying either both or neither of x and y should be given

my ultimate goal is to count true positive , true negatives , FP and FN , based on cluster and class label. this is the step towards..

EdChum · Accepted Answer · 2015-05-08 07:36:49Z

2

Call map and pass the dict:

In [326]:

d={'cluster2': 'Iris-virginica', 'cluster0': 'Iris-versicolor', 'cluster1': 'Iris-setosa'}
df['key'] = df['cluster'].map(d)
df
Out[326]:
   sepallength  sepalwidth  petallength  petalwidth        class   cluster  \
0          5.1         3.5          1.4         0.2  Iris-setosa  cluster1   
1          4.9         3.0          1.4         0.2  Iris-setosa  cluster1   
2          4.7         3.2          1.3         0.2  Iris-setosa  cluster1   
3          4.6         3.1          1.5         0.2  Iris-setosa  cluster1   
4          5.0         3.6          1.4         0.2  Iris-setosa  cluster1   
5          5.4         3.9          1.7         0.4  Iris-setosa  cluster1   
6          4.6         3.4          1.4         0.3  Iris-setosa  cluster1   
7          5.0         3.4          1.5         0.2  Iris-setosa  cluster1   
8          4.4         2.9          1.4         0.2  Iris-setosa  cluster1   
9          4.9         3.1          1.5         0.1  Iris-setosa  cluster1   

           key  
0  Iris-setosa  
1  Iris-setosa  
2  Iris-setosa  
3  Iris-setosa  
4  Iris-setosa  
5  Iris-setosa  
6  Iris-setosa  
7  Iris-setosa  
8  Iris-setosa  
9  Iris-setosa

answered May 8, 2015 at 7:36

EdChum

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2 Comments

swati saoji Over a year ago

Great @EdChum you always have the answer and you understand the questions :+1 . I usually look into documentation of the pandas , but am not able to pick up exactly what i need and land up taking rather a convoluted approach. Is there any book/ reference which would help me train myself in pandas data manipulation.

EdChum Over a year ago

There is wes's book and also the online cookbook, to be honest like with everything the thing is to try. I don't use pandas professionally but I try to answer questions as best I can and have learned from the other pandas users and devs.

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