DDMA Level III
Python Data Visualisation flashcards
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Review every card in this deck. Open any card to reveal its answer. The first 10 are free; the other 39 come with the subject.
How does Python mark out a block of code, and what happens if the indentation is inconsistent?
Python uses indentation, not braces, to define blocks of code. An inconsistently indented block is a syntax error, not just a style problem.
When should you use the interactive interpreter, and when should you run a script?
Interactive interpreter: type and run one statement at a time, best for quick, one-off checks. Script from the command line: run a complete .py file, the standard way to run a finished, repeatable program.
What is the difference between a pandas Series and a DataFrame?
Series: a one-dimensional labelled array, like a single column. DataFrame: a two-dimensional labelled table, like a spreadsheet, and pandas' primary data structure.
How do merging, grouping and concatenating data differ?
Merging: combines two DataFrames based on a shared key column, like a SQL join. Concatenating: stacks DataFrames together, by row or by column. Grouping: splits one dataset into groups by a column's values, to summarise each group separately.
In a basic matplotlib line chart, what do plt.xlabel(), plt.ylabel(), label= and plt.legend() each do?
plt.xlabel() and plt.ylabel() set the axis titles. The string passed to label= (e.g. label='Sales') becomes the series' legend entry. plt.legend() displays that legend, and plt.show() draws the chart.
Which chart suits each question: a relationship, comparing distributions, a correlation matrix, change over time?
Relationship between two continuous variables: scatter plot. Comparing distributions across groups: box plot. Correlation matrix: heat map. Anything changing over time: time series chart.
What is a bubble chart?
A scatter plot where a third variable is encoded as the size of each point.
What is chart presentation style, and how can it be applied in matplotlib?
Consistent fonts, colours and layout across a set of charts. It can be applied with a matplotlib style sheet.
Using the statistics module, what do mean(), median() and mode() return for data = [2, 4, 4, 6, 9]?
stats.mean(data) returns 5 (25 / 5). stats.median(data) returns 4, the middle value. stats.mode(data) returns 4, the most frequent value.
What does a p-value indicate, and how is a small one read?
How likely the observed data would be if there were truly no effect. A small p-value, conventionally below 0.05, is evidence against that no-effect assumption.
What kind of language is Python, and why has it come to dominate data science work?
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What is the difference between a keyword and an identifier?
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What is the difference between a statement and a comment in Python?
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What does a variable hold, and which data types does the guide name?
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What is type conversion? Give the guide's example.
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What do input(), print() and import do?
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Which arithmetic operators and loops does the guide list?
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What is script mode programming?
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How can one Python statement continue over more than one line?
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What is PEP 8?
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What is a Python library?
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How do scrapy and BeautifulSoup differ as data acquisition libraries?
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What does installing Python involve?
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Why add Python's install location to the system PATH?
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What do PYTHONPATH and PYTHONHOME set?
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What do PYTHONSTARTUP and PYTHONCASEOK do?
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What is an integrated development environment (IDE)? Name examples from the guide.
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Which libraries does the SciPy stack bring in, and how is it typically installed?
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What is NumPy's ndarray?
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In what sense is NumPy a replacement for MATLAB?
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What are the key features of pandas?
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What is a pandas Panel, and what replaced it?
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How are SciPy's sub-packages organised? Give two examples.
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What is data cleansing, and why does it come before analysis?
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Which pandas functions read a CSV file and an Excel file into a DataFrame?
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What is data aggregation in Python?
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What must be done with unstructured data before it can be analysed like a clean DataFrame?
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What chart properties are added after a chart is created, and what does each do?
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What does a box plot show, and how is one drawn in matplotlib?
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What does a heat map show, and what is it useful for?
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What does a scatter plot show?
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Why are 3D charts used sparingly?
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What do a time series chart, a geographical chart and a graph (network) chart each show?
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How do statistics.stdev() and numpy.std() differ?
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What does skewness measure, and which function computes it?
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Which scipy.stats objects model the normal, binomial, Poisson and Bernoulli distributions, and what does each model?
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Which functions compute correlation, and what range does it take?
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What does the chi-square test check, and which scipy function runs it?
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How is a linear regression fitted with scipy, and what does it give for x = [1, 2, 3, 4, 5], y = [2, 4, 5, 4, 5]?
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