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Top Questions People Ask About Pandas, NumPy, Matplotlib & Scikit-learn — Answered!

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 Whether you're a beginner or brushing up on your skills, these are the real-world questions Python learners ask most about key libraries in data science. Let’s dive in! 🐍 🐼 Pandas: Data Manipulation Made Easy 1. How do I handle missing data in a DataFrame? df.fillna( 0 ) # Replace NaNs with 0 df.dropna() # Remove rows with NaNs df.isna(). sum () # Count missing values per column 2. How can I merge or join two DataFrames? pd.merge(df1, df2, on= 'id' , how= 'inner' ) # inner, left, right, outer 3. What is the difference between loc[] and iloc[] ? loc[] uses labels (e.g., column names) iloc[] uses integer positions df.loc[ 0 , 'name' ] # label-based df.iloc[ 0 , 1 ] # index-based 4. How do I group data and perform aggregation? df.groupby( 'category' )[ 'sales' ]. sum () 5. How can I convert a column to datetime format? df[ 'date' ] = pd.to_datetime(df[ 'date' ]) ...
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Python - How to Lookup Dictionary by Key

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Here's Python Dictionary that explained how to lookup it using Key. Dictionary in Python is Key/Value pair. It's different from the list. The basic rule to identify; is enclosed in flower brackets ({}). Here's a demo about lookup and how to test it. 


Dictionary = { 'key' : 'value', 'key: value'  }  


Dictionary Lookup


IN THIS PAGE

  1. Python Dictionary
  2. Python Lookup
  3. How to check Lookup working or not

Dictionary


Example

my_dict = {'name' : 'srini' , 'salary' : '100000', 'skills' : 'python' }

Here, 'name' is the label.

Then, :

Then, 'srini' -> Value

Explanation
  • Data is enclosed in flower brackets
  • It's an unordered list
  • You can manipulate data (mutable)
  • You can access the value of a particular key. So, in Python, it's called a Lookup. It's one of the best interview questions.



Lookup Dictionary by Key

Python Lookup (a.k.a Dictionary). You can access data quickly. It's really super-speed. 

my_dict['name']

The result will be: 'srini'

  • You should use square brackets ([]) to get lookup data
  • Use key-value in square brackets ([]) with a single quote, you will get value


Output from Lookup

I am now adding new value to the Lookup.

>>> my_dict['role'] = 'Manager'

Now, the my_dict will'be :

>>> my_dict = {'name' : 'srini' , 'salary' : '100000', 'skills' : 'python' , 'role' : 'Manager'}

  • The order of assignmenet will not match with actula storing in Python
  • The order of Key/Value storage is taken care by interpreter

References

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