Pandas and Matplotlib: df s
is a DataFrame;
is a Series.
Function
Description
df[col]
Returns the column labeled col from df as Series
df[[col1, col2]]
Returns a DataFrame containing the columns labeled col1 and col2.
s.loc[rows] / df.loc[rows, cols]
Returns a Series/DataFrame with rows (and columns) selected by their index values.
s.iloc[rows] / df.iloc[rows, cols]
Returns a Series/DataFrame with rows (and columns) selected by their positions.
s.isnull() / df.isnull()
Returns boolean Series/DataFrame identifying missing values
s.fillna(value) / df.fillna(value)
Returns a Series/DataFrame where missing values are replaced by value
df.drop(labels, axis)
Returns a DataFrame without the rows or columns named labels along axis (either 0 or 1)
Returns a DataFrame with renamed columns from a dictionary index and/or columns
df.rename(index=None, columns=None)
df.sort_values(by, ascending=True)
Returns a DataFrame where rows are sorted by the values in columns by
s.sort_values(ascending=True)
Returns a sorted Series.
s.unique()
Returns a NumPy array of the unique values
s.value_counts()
Returns the number of times each unique value appears in a Series
pd.merge(left, right, how=’inner’, on=’a’)
Returns a DataFrame joining DataFrames left and right on the column labeled a; the join is of type inner
left.merge(right, left_on=col1, right_on=col2)
Returns a DataFrame joining DataFrames left and right on columns labeled col1 and col2.
df.set_index(col)
Returns a DataFrame that uses the values in the column labeled col as the row index.
df.reset_index(col)
Returns a DataFrame that has row index 0, 1, etc., and adds the current index as a column.
w
here by
can be a column label or a list of labels.
Function
Description
grouped.count()
Return a Series containing the size of each group, excluding missing values
grouped.size()
Return a Series containing size of each group, including missing values
Return a Series/DataFrame containing mean/min/max of each group for each column, excluding missing values
grouped.mean()/grouped.min()/grouped.max()
grouped.first()/grouped.last()
Return a Series/DataFrame containing first/last element of each group for each column
Filters or aggregates using the given function f
grouped.filter(f)/grouped.agg(f)
Groups: grouped = df.groupby(by)
Strings: s is a series of strings.
Function
Description
s.str.len()
Returns a Series containing length of each string
s.str.lower()/s.str.upper()
Returns a Series containing lowercase/uppercase version of each string
s.str.replace(pat, repl)
Returns a Series after replacing occurences of substrings matching regular expression pat with string repl
s.str.contains(pat)
Returns a boolean Series indicating whether a substring matching the regular expression pat is contained in each string
s.str.extract(pat)
Returns a Series of the first subsequence of each string that matches the regular expression pat. If pat contains one group, then only the substring matching the group is extracted
Plotting: x and y are sequences of values.
Function
Description
plt.plot(x, y)
Creates a line plot of x against y
plt.scatter(x, y)
Creates a scatter plot of x against y
plt.hist(x, bins=None)
Creates a histogram of x; bins can be an integer or a sequence
plt.bar(x, height)
Creates a bar plot of categories x and corresponding heights height
Regular Expressions:
List of all metacharacters: . ^ $ * + ? ] [ | ( ) { }
Operator
Description
.
Matches any character except
Escapes metacharacters
|
Matches expression on either side of expression; has lowest priority of any operator
d, w, s
Predefined character group of digits (0-9), alphanumerics (a-z, A-Z, 0-9, and underscore), or whitespace, respectively
D, W, S
Inverse sets of d, w, s, respectively
*
Matches preceding character/group zero or more times
?
Matches preceding character/group zero or one times
+
Matches preceding character/group one or more times
*?, +?
Applies non-greedy matching to * and +, respectively
{m}
Matches preceding character/group exactly m times
{m, n}
Matches preceding character/group at least m times and at most n times; if either m or n are omitted, set lower/upper bounds to 0 and ¡Þ, respectively
^, $
Matches the beginning and end of the line, respectively
[]
Matching group used to match any of the specified characters or range (e.g. [abcde]) [a-e])
()
Capturing group used to create a sub-expression
[^ ]
Invert matching group; e.g. [^a-c] matches all characters except a, b, c
Regex String Matching:
Function
Description
re.match(pattern, string)
Returns a match if zero or more characters at beginning of string matches pattern, else None
re.search(pattern, string)
Returns a match if zero or more characters anywhere in string matches pattern, else None
re.findall(pattern, string)
Returns a list of all non-overlapping matches
of pattern in string (if none, returns empty list)
re.sub(pattern, repl, string)
Returns string after replacing all occurrences of pattern with repl
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