OpenEDG PCED — Certified Entry-Level Data Analyst with Python

Which Python data structure is most appropriate for storing column-oriented tabular data with labeled rows and columns?

• Alist
• Bdict
• Cnumpy.ndarray
• Dpandas.DataFrame

What is the canonical alias used when importing pandas in data-analysis code?

• Aimport pandas as pn
• Bimport pandas as pd
• Cimport pandas as ps
• Dimport pd from pandas

Which built-in Python function reads a text file line by line in a memory-efficient way using a context manager?

• Aopen(path).readlines()
• Bwith open(path) as f: for line in f
• Cfile.readall()
• Dio.read_lines(path)

Which standard-library module is used to read and write CSV files when you do not want to load the file into a DataFrame?

• Ajson
• Bcsv
• Cpickle
• Dio

What does `np.arange(2, 10, 2)` return?

• Aarray([2, 4, 6, 8])
• Barray([2, 4, 6, 8, 10])
• Carray([2, 10, 2])
• Darray([0, 2, 4, 6, 8])

How many elements does `np.linspace(0, 1, 5)` produce?

• A4
• B5
• C6
• D10

What is the shape of `np.zeros((3, 4))`?

• A(4, 3)
• B(3, 4)
• C(12,)
• D(3,)

Which ndarray attribute returns the number of dimensions of an array?

• Aarr.shape
• Barr.size
• Carr.ndim
• Darr.dtype

Given `a = np.array([[1, 2, 3], [4, 5, 6]])`, what is `a.shape`?

• A(2, 3)
• B(3, 2)
• C(6,)
• D(1, 6)

Which dtype does `np.array([1, 2, 3, 4])` use by default on a 64-bit system?

• Aint8
• Bint32
• Cint64
• Dfloat64

Given `a = np.arange(12).reshape(3, 4)`, what does `a[1, 2]` return?

• A5
• B6
• C7
• DAn error — multi-dimensional indexing requires a tuple

Given `a = np.arange(10)`, what does `a[2:8:2]` return?

• Aarray([2, 4, 6])
• Barray([2, 4, 6, 8])
• Carray([2, 3, 4, 5, 6, 7])
• Darray([2, 8, 2])

Given `a = np.array([10, 20, 30, 40])`, what does `a[a > 15]` return?

• Aarray([True, True, True, True])
• Barray([20, 30, 40])
• Carray([10, 20, 30, 40])
• DAn IndexError

What is the difference between `arr.ravel()` and `arr.flatten()`?

• AThey are identical
• Bravel() returns a view when possible, flatten() always returns a copy
• Cflatten() returns a view, ravel() always returns a copy
• Dravel() works only on 1-D arrays

Given a NumPy array of shape (3, 4), which call produces a transposed array of shape (4, 3)?

• Aa.reshape(4, 3)
• Ba.T
• Ca.flatten().reshape(4, 3)
• Dnp.swap(a)

What does `np.arange(6).reshape(2, 3) + np.array([10, 20, 30])` produce?

• AA ValueError due to shape mismatch
• Barray([[10, 21, 32], [13, 24, 35]])
• Carray([[10, 21, 32], [40, 51, 62]])
• Darray([[10, 22, 33], [40, 51, 62]])

Which broadcasting rule allows `np.zeros((3, 4)) + np.ones((4,))` to succeed?

• ABoth arrays must have the same number of dimensions
• BTrailing dimensions must be equal or one of them must be 1
• CArrays must have the same total number of elements
• DBroadcasting only works when the second operand is a scalar

Given `a = np.array([[1, 2], [3, 4]])`, what does `a.sum(axis=0)` return?

• Aarray([3, 7])
• Barray([4, 6])
• C10
• Darray([[1, 2], [3, 4]])

Which NumPy function returns the index of the maximum value in an array?

• Anp.max
• Bnp.argmax
• Cnp.maximum
• Dnp.where_max

What does `np.where(a > 0, 1, -1)` do for an integer array `a`?

• AReturns a new array with 1 where a > 0 and -1 elsewhere
• BModifies a in place, replacing values greater than 0 with 1
• CReturns the indices where a > 0
• DRaises an error because where requires only one condition

What does `np.array([3, 1, 2]).cumsum()` return?

• Aarray([6])
• Barray([3, 4, 6])
• Carray([1, 2, 3])
• Darray([3, 1, 2])

Which of the following correctly computes the sample standard deviation (Bessel-corrected) of a NumPy array?

• Aa.std()
• Ba.std(ddof=0)
• Ca.std(ddof=1)
• Dnp.std_sample(a)

Which pandas object is 1-dimensional with an index?

• ADataFrame
• BSeries
• CPanel
• DIndex

Which call reads a comma-separated file into a DataFrame, treating the first row as headers?

• Apd.read_csv('file.csv')
• Bpd.read_csv('file.csv', header=None)
• Cpd.load_csv('file.csv')
• Dpd.DataFrame.from_csv('file.csv')

Which argument in `pd.read_csv` lets you read only specific columns from a wide CSV file?

• Acolumns
• Busecols
• Cselect
• Dcols

Which method writes a DataFrame to a CSV file without including the index column?

• Adf.to_csv('out.csv', drop_index=True)
• Bdf.to_csv('out.csv', index=False)
• Cdf.write_csv('out.csv')
• Ddf.save_csv('out.csv', no_index=True)

What is the difference between `df.loc` and `df.iloc`?

• Aloc selects by label/condition; iloc selects by integer position
• BThey are identical
• Cloc only selects rows; iloc only selects columns
• Diloc supports boolean indexing; loc does not

Which expression returns the first 3 rows of a DataFrame `df`?

• Adf.first(3)
• Bdf.head(3)
• Cdf[1:3]
• Ddf.top(3)

How do you select all rows where the 'age' column is greater than 30?

• Adf.where(df.age > 30)
• Bdf[df.age > 30]
• Cdf.loc[df.age > 30]
• DBoth B and C

Which method tests for missing values in a pandas Series or DataFrame?

• Aisnull()
• Bisna()
• CBoth isna() and isnull() (they are aliases)
• Dmissing()

Which call removes any row that contains at least one missing value?

• Adf.dropna()
• Bdf.dropna(how='all')
• Cdf.fillna()
• Ddf.drop()

Which call replaces every missing value in column 'price' with the column's median?

• Adf.price = df.price.fillna(df.price.median())
• Bdf.fillna(median)
• Cdf.price.replace(NaN, median)
• Ddf.price.dropna(replace=median)

Which method removes duplicate rows from a DataFrame?

• Adf.unique()
• Bdf.drop_duplicates()
• Cdf.distinct()
• Ddf.dedupe()

Which call renames the column 'old_name' to 'new_name' WITHOUT modifying df in place?

• Adf.rename({'old_name': 'new_name'})
• Bdf.rename(columns={'old_name': 'new_name'})
• Cdf.columns = ['new_name']
• Ddf.rename(old='old_name', new='new_name')

Which call converts the column 'date_str' from string to datetime?

• Adf.date_str.to_datetime()
• Bpd.to_datetime(df.date_str)
• Cdf.date_str.astype('datetime')
• Ddatetime.parse(df.date_str)

After `df['date'] = pd.to_datetime(df['date'])`, how do you extract the year of each row?

• Adf.date.year
• Bdf.date.dt.year
• Cdf.date.get_year()
• Dyear(df.date)

Which call computes the mean of column 'sales' for each value of column 'region'?

• Adf.groupby('region')['sales'].mean()
• Bdf.mean('region', 'sales')
• Cdf.aggregate('region', 'sales')
• Ddf.region.sales.mean()

Which call computes BOTH the mean AND the sum of 'sales' per 'region' in one expression?

• Adf.groupby('region')['sales'].agg(['mean', 'sum'])
• Bdf.groupby('region').mean().sum()
• Cdf.groupby('region')['sales'].mean_sum()
• Ddf.groupby('region', agg=['mean', 'sum'])

Which groupby method broadcasts each group's aggregate back to its original row positions, preserving DataFrame shape?

• Aagg
• Bapply
• Ctransform
• Dfilter

Which function performs an SQL-style INNER join between two DataFrames on the 'id' column?

• Apd.merge(left, right, on='id', how='inner')
• Bpd.concat([left, right], axis=1)
• Cleft.append(right)
• Dpd.join(left, right, on='id')

Which call stacks two DataFrames vertically, aligning columns by name?

• Apd.merge(df1, df2)
• Bpd.concat([df1, df2], axis=0)
• Cpd.concat([df1, df2], axis=1)
• Ddf1.join(df2)

Which call reshapes a long-format DataFrame so each unique value of 'category' becomes its own column, with 'value' as the cell content?

• Adf.melt(id_vars='id', value_vars='category')
• Bdf.pivot(index='id', columns='category', values='value')
• Cdf.transpose()
• Ddf.reset_index()

What does `df.melt(id_vars=['id'], value_vars=['col1', 'col2'])` produce?

• AA wide DataFrame with one row per id
• BA long DataFrame with columns: id, variable, value
• CA DataFrame with col1 and col2 swapped
• DAn error — melt requires only one value_var

Which call sorts a DataFrame by the 'price' column in descending order?

• Adf.sort_values('price', ascending=False)
• Bdf.sort('price', desc=True)
• Cdf.order_by('price desc')
• Ddf.sort_values('price').reverse()

Which call changes the dtype of column 'count' to integer?

• Adf['count'] = df['count'].astype(int)
• Bdf['count'].convert(int)
• Cdf['count'].cast('int')
• Dint(df['count'])

Which function summarises a numeric DataFrame's count, mean, std, min, quartiles, and max in one call?

• Adf.summary()
• Bdf.describe()
• Cdf.stats()
• Ddf.info()

What does `df.info()` show?

• AFirst 5 rows
• BNumeric statistics
• CIndex dtype, column names, dtypes, non-null counts, memory usage
• DCorrelation matrix