Python Reference

String Methods

Name Chapter Description
str.split(separator) N/A Splits the string str into a list based on the string separator that is passed in
str.join(array) N/A Combines each element of array into one string, with string str being placed in between each element of array
str.replace(old_string, new_string) Ch 4.2 Replaces each occurrence of old_string in str with the value of new_string

Array Functions and Methods

Name Chapter Description
max(array) Ch 3.3 Returns the maximum value of an array
min(array) Ch 3.3 Returns the minimum value of an array
sum(array) Ch 3.3 Returns the sum of the values in an array
abs(num)
np.abs(array)
Ch 3.3 Take the absolute value of number or each number in an array
round(num)
np.round(array)
Ch 3.3 Round number or array of numbers to the nearest integer
len(array) Ch 3.3 Returns the length (number of elements) of an array
make_array(val1, val2, ...) Ch 5 Makes a numpy array with the values passed in
np.average(array)
np.mean(array)
Ch 5.1 Returns the mean value of an array
np.diff(array) Ch 5.1 Returns a new array of size len(arr)-1 with elements equal to the difference between adjacent elements; val_2 - val_1, val_3 - val_2, etc.
np.sqrt(array) Ch 5.1 Returns an array with the square root of each element
np.arange(stop)
np.arange(start, stop)
np.arange(start, stop, step)
Ch 5.2 An array of numbers starting with start, going up in increments of step, and going up to but not including stop. When start and/or step are left out, default values are used in their place. The default for step is 1 and the default for start is 0.
array.item(index) Ch 5.3 Returns the i-th item in an array (remember Python indices start at 0!)

Table Functions and Methods

In the examples in the left column, np refers to the NumPy module, as usual. Everything else is a function, a method, an example of an argument to a function or method, or an example of an object we might call the method on. For example, tbl refers to a table, array refers to an array, and num refers to a number. array.item(0) is an example call for the method item, and in that example, array is the name previously given to some array.

Name Chapter Description Input Output
Table() Ch 6 Create an empty table, usually to extend with data None
Table().read_table(filename) Ch 6 Create a table from a data file filename (string): the name of the file Table with the contents of the data file
tbl.with_columns(name, values)
tbl.with_columns(n1, v1, n2, v2,...)
Ch 6 Create a table with an additional or replaced column or columns name (string): the name of the new column
array: the values in that column
Table: a copy of the original Table with the new columns added
tbl.column(column_name_or_index) Ch 6 Give the values of a column as an array column_name_or_index (string or int): the column name or index array: the values in the specified column
tbl.num_rows Ch 6 Compute the number of rows in a table None int: the number of rows in the table
tbl.num_columns Ch 6 Compute the number of columns in a table None int: the number of columns in the table
tbl.labels Ch 6 List the column labels in a table None array: the names of each column (as strings) in the table
tbl.select(col1, col2, ...) Ch 6 Create a copy of a table with only some of the columns where each column is the column name or index col (string or int): column name(s) or index(es) Table with the selected columns
tbl.drop(col1, col2, ...) Ch 6 Create a copy of a table without some of the columns where each column is the column name or index col (string or int}: column name(s) or index(es) Table without the selected columns
tbl.relabel(old_label, new_label) Ch 6 Modify the existing table in place, changing the column heading in the first argument to the second old_label (string) the old column name
new_label (string) the new column name
Table: a copy of the original with the changed label
tbl.show(n) Ch 6.1 Display n rows of a table; if no argument is specified, defaults to displaying the entire table n (int, optional): number of rows to display None: displays a table with n rows
tbl.sort(column_name_or_index) Ch 6.1 Create a copy of a table sorted by the values in a column; defaults to ascending order unless descending = True is included column_name_or_index (string or int): the column name or index
descending = True (optional): sort in descending order
Table: a copy of the original with the column sorted
tbl.where(column, predicate) Ch 6.2 Create a copy of a table with only the rows that match some predicate (see Table.where predicates below) column (string or int): column name or index
predicate: a Table.where predicate
Table: a copy of the original table with only the rows that match the predicate
tbl.take(row_indices) Ch 6.2 A table with only the rows at the given indices row_indices (array or int): an array indices of the rows to be included in the Table or in the case of an int, the for index of the row to be included Table: a copy of the original table with only the rows at the given indices
tbl.scatter(x_column, y_column) Ch 7 Draws a scatter plot consisting of one point for each row of the table; note that x_column and y_column must be strings specifying column names x_column (string): name of the column on the x-axis
y_column (string): name of the column on the y-axis
None: draws a scatter plot
tbl.plot(x_column, y_column) Ch 7 Draw a line graph consisting of one point for each row of the table x_column (string): name of the column on the x-axis
y_column (string): name of the column on the y-axis
None: draws a line graph
tbl.barh(categories)
tbl.barh(categories, values)
Ch 7.1 Displays a bar chart with bars for each category in a column, with height proportional to the corresponding frequency; values argument unnecessary if table has only a column of categories and a column of values categories (string): name of the column with categories
values (string, optional): the name of the column with values for corresponding categories
None: draws a bar chart
tbl.hist(column, unit, bins) Ch 7.2 Generates a histogram of the numerical values in a column. unit and bins are optional arguments, used to label the axes and group the values into intervals (bins), respectively; bins have the form [a, b), where a is included in the bin and b is not column (string): name of the column with categories
unit (string, optional): units of x-axis
bins (array of ints or floats, optional): denotes bin boundaries
None: draws a histogram

Table.where Predicates

Any of these predicates can be negated by adding not_ in front of them, e.g., are.not_equal_to(Z) or are.not_containing(S).

Predicate Description
are.equal_to(Z) Equal to Z
are.above(x) Greater than x
are.above_or_equal_to(x) Greater than or equal to x
are.below(x) Less than x
are.below_or_equal_to(x) Less than or equal to x
are.between(x,y) Greater than or equal to x and less than y
are.between_or_equal_to(x,y) Greater than or equal to x, and less than or equal to y
are.contained_in(A) Is a substring of A (if A is a string) or an element of A (if A is an array)
are.containing(S) Contains the string S
are.strictly_between(x,y) Greater than x and less than y