python - Create new column and put conditional value pandas dataframe -

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 dictionary :

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

i need add column , fill values dictionary of df['cluster'] == key

i have tried using np.where

def counttruth(df):     # dictionary mapping cluster frequent class      clustersclass = df.groupby(['cluster'])['class'].agg(lambda x:x.value_counts().index[0]).to_dict()     eachkey in clustersclass:         newv = clustersclass[eachkey]         print df         df['new'] = np.where(df['cluster']==eachkey , newv)  

crashes saying either both or neither of x , y should given

my ultimate goal count true positive , true negatives , fp , fn , based on cluster , class label. step towards..

call map , pass 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