Pig Latin basics in Hadoop - Mini Project: Build & Apply

Pig Latin basics

📖 Scenario: You work at a small company that collects sales data. You want to use Pig Latin to analyze this data easily.

🎯 Goal: Learn how to load data, filter it, and display results using Pig Latin.

📋 What You'll Learn

Create a relation with sales data

Add a filter condition

Use a foreach statement to select fields

Display the final filtered data

💡 Why This Matters

🌍 Real World

Pig Latin is used to process large datasets in Hadoop environments for data analysis.

💼 Career

Knowing Pig Latin helps in roles like data engineer or big data analyst working with Hadoop.

1

Create the sales data relation

Create a relation called sales with these exact tuples: ("Alice", 300), ("Bob", 150), ("Charlie", 200) using the LOAD statement with PigStorage and schema (name:chararray, amount:int).

Hadoop

# Create the sales relation with the given data

Hint

Use LOAD with PigStorage and define the schema with AS.

2

Filter sales greater than 180

Create a relation called big_sales by filtering sales where amount is greater than 180 using the FILTER statement.

Hadoop

sales = LOAD 'data.txt' USING PigStorage(',') AS (name:chararray, amount:int);
# Filter sales with amount > 180

Hint

Use FILTER with the condition amount > 180.

3

Select name and amount from filtered data

Create a relation called result using FOREACH on big_sales to generate only the name and amount fields.

Hadoop

sales = LOAD 'data.txt' USING PigStorage(',') AS (name:chararray, amount:int);
big_sales = FILTER sales BY amount > 180;
# Select name and amount from big_sales

Hint

Use FOREACH with GENERATE to select fields.

4

Display the filtered sales data

Use the DUMP statement to display the contents of the result relation.

Hadoop

sales = LOAD 'data.txt' USING PigStorage(',') AS (name:chararray, amount:int);
big_sales = FILTER sales BY amount > 180;
result = FOREACH big_sales GENERATE name, amount;
# Display the result

Hint

Use DUMP result; to see the filtered data.

Practice

1. What is the main purpose of the FILTER statement in Pig Latin?

easy

A. To select rows that meet a condition

B. To combine two datasets

C. To load data from a file

D. To save the results to storage

Solution

1. Step 1: Understand the role of FILTER

   The FILTER statement is used to keep only the rows that satisfy a given condition.

2. Step 2: Compare with other statements

   LOAD reads data, GROUP groups data, STORE saves data, so FILTER is for selecting rows.

3. Final Answer:

   To select rows that meet a condition -> Option A

4. Quick Check:

   FILTER = select rows [OK]

Hint: FILTER keeps rows matching condition, like a sieve [OK]

Common Mistakes:

• Confusing FILTER with GROUP
• Thinking FILTER saves data
• Mixing FILTER with LOAD

2. Which of the following is the correct syntax to load a file named data.txt in Pig Latin?

easy

A. LOAD 'data.txt' USING PigStorage();

B. LOAD data.txt USING PigStorage();

C. LOAD 'data.txt' AS PigStorage();

D. LOAD 'data.txt' USING PigStorage

Solution

1. Step 1: Check the LOAD syntax

   LOAD requires the file path as a string in quotes and the loader function with parentheses.

2. Step 2: Validate each option

   LOAD 'data.txt' USING PigStorage(); uses quotes and parentheses correctly. LOAD data.txt USING PigStorage(); misses quotes. LOAD 'data.txt' AS PigStorage(); uses AS instead of USING. LOAD 'data.txt' USING PigStorage misses parentheses.

3. Final Answer:

   LOAD 'data.txt' USING PigStorage(); -> Option A

4. Quick Check:

   LOAD 'file' USING loader(); [OK]

Hint: LOAD needs quotes and parentheses for loader [OK]

Common Mistakes:

• Forgetting quotes around filename
• Using AS instead of USING
• Omitting parentheses after loader

3. Given the following Pig Latin code:

A = LOAD 'numbers.txt' USING PigStorage(',');
B = FILTER A BY $0 > 10;
C = FOREACH B GENERATE $0;
DUMP C;

What will be the output if numbers.txt contains:
5,abc
15,def
8,ghi
20,jkl

medium

A. (5,abc)
(8,ghi)

B. (5)
(8)

C. (15,def)
(20,jkl)

D. (15)
(20)

Solution

1. Step 1: Understand the FILTER condition

   FILTER keeps rows where first column ($0) is greater than 10, so rows with 15 and 20 remain.

2. Step 2: Understand FOREACH GENERATE

   FOREACH selects only the first column ($0), so output shows only 15 and 20 as single values.

3. Final Answer:

   (15) (20) -> Option D

4. Quick Check:

   FILTER $0 > 10 then select $0 [OK]

Hint: FILTER then FOREACH select column shows filtered values [OK]

Common Mistakes:

• Including second column in output
• Selecting rows less than or equal to 10
• Confusing FILTER condition

4. Identify the error in this Pig Latin script:

data = LOAD 'input.txt' USING PigStorage(',');
filtered = FILTER data BY $1 == 'USA';
grouped = GROUP filtered BY $2;
result = FOREACH grouped GENERATE group, COUNT(filtered);
STORE result INTO 'output';

medium

A. COUNT should use filtered instead of group

B. STORE command missing USING clause

C. FILTER condition uses wrong column index

D. GROUP should use filtered instead of data

Solution

1. Step 1: Check STORE syntax

   STORE requires a USING clause to specify the storage format, e.g., PigStorage().

2. Step 2: Verify other statements

   GROUP uses filtered correctly, COUNT uses filtered correctly, FILTER condition is valid if $1 is country column.

3. Final Answer:

   STORE command missing USING clause -> Option B

4. Quick Check:

   STORE ... INTO 'path' USING loader() [OK]

Hint: STORE needs USING clause to save data [OK]

Common Mistakes:

• Omitting USING in STORE
• Confusing GROUP input
• Misunderstanding COUNT argument

5. You have a dataset of sales with columns: product_id, region, amount. You want to find total sales per region but only for sales above 100. Which Pig Latin sequence correctly achieves this?

hard

A. A = LOAD 'sales.txt' USING PigStorage(',');
B = FILTER A BY amount > 100;
C = GROUP B BY region;
D = FOREACH C GENERATE group, SUM(B.amount);
STORE D INTO 'result' USING PigStorage();

B. A = LOAD 'sales.txt' USING PigStorage(',');
B = FILTER A BY $2 > 100;
C = GROUP B BY $1;
D = FOREACH C GENERATE group, SUM(B.$2);
STORE D INTO 'result';

C. A = LOAD 'sales.txt' USING PigStorage(',');
B = FILTER A BY $2 > 100;
C = GROUP B BY $1;
D = FOREACH C GENERATE group, SUM(B.$2);
STORE D INTO 'result' USING PigStorage();

D. A = LOAD 'sales.txt' USING PigStorage(',');
B = FILTER A BY $1 > 100;
C = GROUP B BY $2;
D = FOREACH C GENERATE group, SUM(B.$3);
STORE D INTO 'result' USING PigStorage();

Solution

1. Step 1: Identify correct column indexes

   Columns: product_id ($0), region ($1), amount ($2). Filter by amount > 100 means FILTER BY $2 > 100.

2. Step 2: Group by region and sum amount

   Group by $1 (region), then sum B.$2 (amount) in FOREACH. STORE needs USING clause.

3. Step 3: Check each option

   A = LOAD 'sales.txt' USING PigStorage(','); B = FILTER A BY $2 > 100; C = GROUP B BY $1; D = FOREACH C GENERATE group, SUM(B.$2); STORE D INTO 'result' USING PigStorage(); matches all requirements: correct filter, group, sum, and STORE syntax.

4. Final Answer:

   Option C code sequence -> Option C

5. Quick Check:

   Filter $2>100, group $1, sum $2, STORE with USING [OK]

Hint: Use correct column indexes and STORE with USING [OK]

Common Mistakes:

• Using wrong column indexes for filter or group
• Omitting USING in STORE
• Summing wrong column