String Methods

Name Chapter Description
 str.split(separator) N/A  Splits the string (str) into a list based on the separator that is passed in
 str.join(array) N/A  Combines each element of array into one string, with str being in-between each element
 str.replace(old_string, new_string) 4.2.1  Replaces each occurrence of old_string in str with the value of new_string

Array Functions and Methods

Name Chapter Description
 max(array) 3.3  Returns the maximum value of an array
 min(array) 3.3  Returns the minimum value of an array
 sum(array) 3.3  Returns the sum of the values in an array
 abs(num), np.abs(array) 3.3  Take the absolute value of number or each number in an array.
 round(num), np.round(array) 3.3  Round number or array of numbers to the nearest integer.
 len(array) 3.3  Returns the length (number of elements) of an array
 make_array(val1, val2, ...) 5  Makes a numpy array with the values passed in
 np.average(array) np.mean(array) 5.1  Returns the mean value of an array
 np.std(array) 14.2  Returns the standard deviation of an array
 np.diff(array) 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) 5.1  Returns an array with the square root of each element
 np.arange(start, stop, step)   np.arange(start, stop) np.arange(stop) 5.2  An array of numbers starting with start, going up in increments of step, and going up to but  excluding stop. When start and/or step are left out, default values are used in their place. The default step is 1; the default start is 0.
 array.item(index) 5.3  Returns the i-th item in an array (remember Python indices start at 0!)
 np.random.choice(array, n)   np.random.choice(array)   np.random.choice(array, n, replace) 9  Picks one (by default) or some number ‘n’ of items from an array at random. Default is with replacement. For sampling without replacement, use the argument replace=False.
 np.count_nonzero(array) 9  Returns the number of non-zero (or True) elements in an array.
 np.append(array, item) 9.2  Returns a copy of the input array with item (must be the same type as the other entries in the  array) appended to the end.
 percentile(percentile, array) 13.1  Returns the corresponding percentile of an array.

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() 6  Create an empty table, usually to extend with data  None  An empty Table
 Table().read_table(filename) 6  Create a table from a data file  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,...) 6  A table with an additional or replaced column or columns. name is a string for the name of a column, values is an array  1. string: the name of the new column;
2. array: the values in that column		  Table: a copy of the original Table with the new columns added
 tbl.column(column_name_or_index) 6  The values of a column (an array)  string or int: the column name or index  array: the values in that column
 tbl.num_rows 6  Compute the number of rows in a table  None  int: the number of rows in the table
 tbl.num_columns 6  Compute the number of columns in a table  None  int: the number of columns in the table
 tbl.labels 6  Lists the column labels in a table  None  array: the names of each column (as strings) in the table
 tbl.select(col1, col2, ...) 6  Create a copy of a table with only some of the columns. Each column is the column name or index.  string or int: column name(s) or index(es)  Table with the selected columns
 tbl.drop(col1, col2, ...) 6  Create a copy of a table without some of the columns. Each column is the column name or index.  string or int: column name(s) or index(es)  Table without the selected columns
 tbl.relabel(old_label, new_label) 6  Modifies the existing table in place, changing the column heading in the first argument to the second  1. string: the old column name
2. string: the new column name		  Table: a copy of the original with the changed label
 tbl.show(n) 6.1  Display n rows of a table. If no argument is specified, defaults to displaying the entire table.  (Optional) int: number of rows you want to display  None: displays a table with n rows
 tbl.sort(column_name_or_index) 6.1  Create a copy of a table sorted by the values in a column. Defaults to ascending order unless descending = True is included.  1. string or int: column index or name
2. (Optional) descending = True		  Table: a copy of the original with the column sorted
 tbl.where(column, predicate) 6.2  Create a copy of a table with only the rows that match some predicate See Table.where predicates below.  1. string or int: column name or index
2. are.(...) predicate		  Table: a copy of the original table with only the rows that match the predicate
 tbl.take(row_indices) 6.2  A table with only the rows at the given indices. row_indices is either an array of indices or an integer corresponding to one index.  array of ints: the indices of the rows to be included in the Table OR int: the 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) 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.  1. string: name of the column on the x-axis
2. string: name of the column on the y-axis		  None: draws a scatter plot
 tbl.plot(x_column, y_column) 7  Draw a line graph consisting of one point for each row of the table.  1. string: name of the column on the x-axis
2. string: name of the column on the y-axis		  None: draws a line graph
 tbl.barh(categories)   tbl.barh(categories, values) 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.  1. string: name of the column with categories
2. (Optional) string: the name of the column with values for corresponding categories		  None: draws a bar chart
 tbl.hist(column, unit, bins) 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.  1. string: name of the column with categories
2. (Optional) string: units of x-axis
3. (Optional) array of ints/floats denoting bin boundaries		  None: draws a histogram
 tbl.apply(function, col1, col2, ...) 8.1  Returns an array of values resulting from applying a function to each item in a column.  1. function: function to apply to column
2. (Optional) string: name of the column to apply function to (if you have multiple columns, the respective column’s values will be passed as the corresponding argument to the function), and if there is no argument, your function will be applied to every row in tbl		  array: contains an element for each value in the original column after applying the function to it
 tbl.group(column_or_columns, func) 8.2  Group rows by unique values or combinations of values in a column(s). Multiple columns must be entered in array or list form. Other values aggregated by count (default) or optional argument func.  1. string or array of strings: column(s) on which to group
2. (Optional) function: function to aggregate values in cells (defaults to count)		  Table: a new Table
 tbl.pivot(col1, col2, values,  collect) tbl.pivot(col1, col2) 8.3  A pivot table where each unique value in col1 has its own column and each unique value in col2 has its own row. Count or aggregate values from a third column, collect with some function. Default values and collect return counts in cells.  1. string: name of column whose unique values will make up columns of pivot table
2. string: name of column whose unique values will make up rows of pivot table
3. (Optional) string: name of column that describes the values of cell
4. (Optional) function: how the values are collected, e.g. sum or np.mean		  Table: a new Table
 tblA.join(colA, tblB, colB)   tblA.join(colA, tblB) 8.4  Generate a table with the columns of tblA and tblB, containing rows for all values of a column that appear in both tables. Default colB is colA. colA and colB must be strings specifying column names.  1. string: name of column in tblA with values to join on
2. Table: other Table
3. (Optional) string: if column names are different between Tables, the name of the shared column in tblB		  Table: a new Table
 tbl.sample(n) tbl.sample(n, with_replacement) 10  A new table where n rows are randomly sampled from the original table; by default, n=tbl.num_rows. Default is with replacement. For sampling without replacement, use argument with_replacement=False. For a non-uniform sample, provide a third argument weights=distribution where distribution is an array or list containing the probability of each row.  1. int: sample size
2. (Optional) with_replacement=True		  Table: a new Table with n rows