Array-Select Node

Purpose & Use Cases

The array-select node provides powerful array element selection with Python-like slicing syntax. It extracts specific elements, ranges, or patterns from arrays, making it essential for filtering and selecting processed results.

Real-World Applications:

• Result Filtering: Select best results from batch processing operations
• Data Sampling: Extract samples from large datasets for analysis
• Quality Control: Pick specific items that passed validation
• A/B Testing: Select specific variants for comparison
• Image Gallery Creation: Choose specific images from collections

Input/Output Specification

Inputs

• Array Data: Input array from the configured path
• Selection String: Pattern specifying which elements to extract

Outputs

• Single Element: Direct element output (unless Force Array enabled)
• Multiple Elements: Always output as array
• Invalid Selection: No message sent, warning logged

Configuration Options

Input From

• Default: msg.payload
• Options:
  • msg.* - Read from message property
  • flow.* - Read from flow context
  • global.* - Read from global context
• Validation: Input must be an array

Selection Pattern

• Type: String with flexible syntax
• Formats:
  • Single Index: 0, 2, -1
  • Multiple Indices: 1,3,5 (comma-separated)
  • Range: 1:4 (slice from index 1 to 3)
  • Step Pattern: 0::2 (every 2nd element)
  • Negative Indexing: -1 (last), -2: (last two)

Force Array

• Type: Boolean checkbox
• Default: false
• Behavior: When enabled, single elements output as arrays
• Use Case: Ensure consistent array output format

Performance Notes

Selection Efficiency

• Minimal Memory Copy: Efficient element extraction without full array duplication
• Index Validation: Fast bounds checking with graceful error handling
• Pattern Parsing: Optimized pattern recognition and processing
• Status Display: Real-time selection information and processing state

Error Handling

• Input Validation: Comprehensive array and pattern validation
• Graceful Degradation: Invalid indices skipped with warnings
• Bounds Checking: Out-of-range indices handled safely

Selection Syntax Guide

Basic Selection

Array: ["A", "B", "C", "D", "E"]

0      → "A"         // First element
-1     → "E"         // Last element
1,3    → ["B", "D"]  // Multiple specific indices

Range Selection

Array: ["A", "B", "C", "D", "E"]

1:4    → ["B", "C", "D"]  // Range from 1 to 3
0:3    → ["A", "B", "C"]  // First three elements
-2:    → ["D", "E"]       // Last two elements

Step Patterns

Array: ["A", "B", "C", "D", "E", "F"]

0::2   → ["A", "C", "E"]     // Every 2nd starting at 0
1::2   → ["B", "D", "F"]     // Every 2nd starting at 1
1:5:2  → ["B", "D"]          // Range 1-4, every 2nd

Advanced Patterns

Array: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

::3     → [0, 3, 6, 9]       // Every 3rd element
2:8:2   → [2, 4, 6]          // Range 2-7, step 2
-3:     → [7, 8, 9]          // Last 3 elements
:-3     → [0, 1, 2, 3, 4, 5, 6]  // All but last 3

Real-World Examples

Best Result Selection

[Batch Process] → [Array-Out] → [Array-Select: "0,2,4"] → [Top Results]

Select 1st, 3rd, and 5th results from batch processing.

Quality Control Sampling

[Production Line] → [Array-Out] → [Array-Select: "::10"] → [Quality Check]

Sample every 10th item for quality inspection.

Image Gallery Creation

[Image Array] → [Array-Select: "1:6"] → [Display Gallery]

Select images 2-6 for gallery display.

A/B Test Splitting

[User Array] → [Array-Select: "0::2"] → [Group A]
            → [Array-Select: "1::2"] → [Group B]

Split users into alternating test groups.

Last N Results

[Processing Queue] → [Array-Out] → [Array-Select: "-5:"] → [Recent Results]

Get the last 5 processed items.

Common Issues & Troubleshooting

Invalid Input Type

• Issue: Input is not an array
• Result: Warning logged, message not sent
• Solution: Verify input is array type, use array-out to create arrays

Out of Bounds Indices

• Issue: Selection indices exceed array length
• Result: Invalid indices ignored, partial results returned
• Example: Array length 5, selection "1,3,7" returns elements at indices 1,3 only

Empty Selection Results

• Issue: Selection pattern matches no elements
• Result: Empty array [] output
• Common Cause: Range beyond array bounds

Syntax Errors

• Issue: Invalid selection pattern syntax
• Result: Warning logged, message not sent
• Solution: Verify pattern follows documented syntax