One-Line PySpark Function Meanings
🧰 Basic utilities
| Function / Method | Meaning |
|---|---|
from pyspark.sql.functions import ... | Imports built-in functions from PySpark SQL module. |
.select([...]) | Selects specific columns from the DataFrame. |
.show() after any transformation | Displays the result of the transformation for visual inspection. |
📦Data Loading & Preview
| Method / Parameter | Meaning |
|---|---|
inferSchema=True | Automatically detects the data types of columns. |
header=True | Treats the first row of the file as column headers. |
df.show() | Displays the first 20 rows of the DataFrame. |
df.head(1) | Retrieves the first row as a list of Row objects. |
df.printSchema() | Displays the structure (schema) of the DataFrame. |
📅Date Functions
| Function / Method | Meaning |
|---|---|
dayofmonth(df['Date']) | Extracts the day (1–31) from a date. |
month(df['Date']) | Extracts the month (1–12) from a date. |
year(df['Date']) | Extracts the year (e.g., 2023) from a date. |
weekofyear(df['Date']) | Extracts the week number of the year from a date. |
date_format(df['Date'], 'MMM') | Formats the date into a custom format (e.g., Jan, Feb). |
🧮 Aggregations & Metrics
| Function / Method | Meaning |
|---|---|
withColumn('Year', year(df['Date'])) | Creates a new column 'Year' derived from the 'Date' column. |
groupBy('Year') | Groups the rows by 'Year' column. |
.mean() or .agg({'col':'mean'}) | Computes average of one or more columns. |
.agg({'Sales':'sum'}) | Computes the total sum for the 'Sales' column. |
.agg({'Volume':'max'}) | Finds the maximum value in the 'Volume' column. |
round(mean(df['Close']), 2) | Computes the mean and rounds it to 2 decimal places. |
max(df['Volume']), min(df['Volume']) | Gets maximum or minimum volume across all rows. |
countDistinct(df['Sales']) | Counts unique (distinct) values in the 'Sales' column. |
🧮 Column Math / Derived Columns
| Expression / Method | Meaning |
|---|---|
(df['ForecastUnits'] / df['ActualUnits']) | Creates a new column with ratio of forecast to actual units. |
.alias('Forecast_to_Actual') | Renames the resulting column to a readable name. |
🧠 SQL Queries
| Function / Method | Meaning |
|---|---|
createOrReplaceTempView('table') | Registers DataFrame as a temporary SQL table. |
spark.sql('...') | Executes SQL query on registered temp table. |
SELECT MAX(column) FROM table | SQL syntax to find the maximum value in a column. |
WHERE ActualUnits = (SELECT MAX(ActualUnits)...) | Filters rows that have the maximum actual units. |
🧰🧠Utility & Optimization Methods
| Function / Method | One-Line Meaning |
|---|---|
distinct() | Removes duplicate rows from the DataFrame. |
dropDuplicates(['col1', 'col2']) | Removes duplicate rows based on specific columns. |
selectExpr("colA as newCol") | Selects column(s) using SQL expressions with aliasing. |
withColumnRenamed("old", "new") | Renames a column. |
cache() | Caches the DataFrame in memory for faster access. |
persist() | Stores DataFrame with a specified storage level (memory, disk, etc.). |
repartition(4) | Redistributes rows across a specified number of partitions. |
coalesce(1) | Reduces the number of partitions, often to write a single output file. |
dropna() | Drops rows with null values (alias for na.drop()). |
fillna(value) | Fills null values with the specified value. |
isNull(), isNotNull() | Filters rows with null or non-null values. |
when(...).otherwise(...) (from functions) | Performs conditional logic like SQL CASE WHEN. |
Joins
| Join Type | Why We Need It |
|---|---|
inner | Only matching rows (common records) |
left | Keep all from left, match where possible |
right | Keep all from right, match where possible |
outer | Keep everything from both sides |
left_semi | Filter left rows that exist in right |
left_anti | Filter left rows that don’t exist in right |
crossJoin() | All combinations (use cautiously — can explode rows) |