Dictionary and array are not used in this way either
df=DataFrame(np.random.randn(20,2),columns=["first","second"])
df["first"][df["first"]<-1.5)]=None
Thank you very much
df['first'][df['first']<-1.5)]=None first of all, is this code wrong? Is there an extra parenthesis?
the correct one should be:
df['first'][df['first']<-1.5]=None DataFrame, df ['first'] represents the selected field or column named first, and the extracted column is actually Series
df [' first'] <-1.5 which represents a vectorized comparison of the Series. The final result is a list of Boolean values obtained by comparing each value in the Series with 1.5
so, df'first' <-1.5], the Boolean value of Series is indexed
finally, Df'first' <-1.5] = None, is just scalar assignment
tells you an easy way to understand this
plus a print function to output the value of df ['first'] to see what it is?
print (df ['first'])
print (type (df [' first'])
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