This document introduces how to use the Offline NEAR Selector for dynamic data selection during supervised fine-tuning (SFT) within the DataFlex framework, finding the most close data to the target dataset to improve generalization performance.

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1. Method Overview

The core idea of NEAR is:

• Further encode already tokenized samples into sentence embeddings (e.g., 512‑dim).
• Perform **nearest‑neighbor search ** in the embedding space to obtain each sample’s representativeness score.

Intuition: Closest data for the target dataset

Scoring Formulation

Let the sentence embedding of a sample be $e_i$, and let its $max_K$ nearest neighbors be $\mathcal{N}_K(i)$.

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2. Environment & Dependencies

# DataFlex (recommended: editable install)
git clone https://github.com/OpenDCAI/DataFlex.git
cd DataFlex
pip install -e .

# Common training/inference dependencies (as needed)
pip install llamafactory

# NEAR extras (vector search & progress bars)
pip install faiss-cpu vllm sentence-transformer

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3. Offline Selection

Modify training set, embedding model, and parameters inside DataFlex/src/dataflex/offline_selector/offline_near_selector.py:

if __name__ == "__main__":
    near = offline_near_Selector(
        candidate_path="OpenDCAI/DataFlex-selector-openhermes-10w", # split = train
        query_path="OpenDCAI/DataFlex-selector-openhermes-10w", # split = vaildation
        # It automatically try vllm first, then sentence-transformers
        embed_model="Qwen/Qwen3-Embedding-0.6B",
        # support method:
        #auto(It automatically try vllm first, then sentence-transformers),
        #vllm,
        #sentence-transformer
        embed_method= "auto",
        batch_size=32,
        save_indices_path="top_indices.npy",
        max_K=1000,
        
    )
    near.selector()

Note: model_name is used to encode the already-tokenized text into sentence embeddings (e.g., 1024-dim), supporting both vLLM and sentence-transformer inference.

Output: save as the indices matrix that contain the max_K close data for each query

4. Key Hyperparameters & Tips

Parameter	Typical Range	Meaning & Tips
max_K	64–10000	Upper bound of NN retrieval. Larger = stabler but more costly; balance with data size & VRAM.
model_name	—	Path/name of the sentence encoder (local BERT/USE/SimCSE, etc.).
cache_dir	—	Cache directory for intermediate artifacts and resume‑from‑cache.

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5. Component Config (components.yaml)

Path: DataFlex/src/dataflex/configs/components.yaml

Preset example

near:
    name: near
    params:
      indices_path: ./src/dataflex/offline_selector/top_indices.npy
      cache_dir: ../dataflex_saves/near_output

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6. Dynamic Training Config (LoRA + NEAR)

Example file: DataFlex/examples/train_lora/selectors/near.yaml

### model
model_name_or_path: 
trust_remote_code: true

### method
stage: sft
do_train: true
finetuning_type: lora
lora_target: all
lora_rank: 16
lora_alpha: 8

### dataset
dataset: # training dataset
template: qwen
cutoff_len: 4096
overwrite_cache: true
preprocessing_num_workers: 16

### output
output_dir: ../dataflex_saves
logging_steps: 10
save_steps: 100
plot_loss: true
overwrite_output_dir: true

### train
per_device_train_batch_size: 2
gradient_accumulation_steps: 16
learning_rate: 1.0e-4
num_train_epochs: 1.0
lr_scheduler_type: cosine
warmup_ratio: 0.1
bf16: true

### Dataflex args
train_type: dynamic_select
components_cfg_file: src/dataflex/configs/components.yaml
component_name: near
warmup_step: 400
update_step: 500
update_times: 2

Notes:

• component_name: near enables the NEAR component.
• warmup_step / update_step / update_times decide when and how often to re-select the training subset in each Flex epoch. Total steps are derived from num_train_epochs unless train_step > 0.
• total batch_size=device_number x per_device_train_batch_size x gradient_accumulation_steps

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7. Run Training

FORCE_TORCHRUN=1 DISABLE_VERSION_CHECK=1 dataflex-cli train examples/train_lora/selectors/near.yaml

Note: the above example runs with distributed launch.

During training, NEAR is triggered at scheduled steps: base the sample indice → select the next training subset.

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8. Merge & Export the Model

Same as the Less Selector pipeline.

Config file: DataFlex/examples/merge_lora/llama3_lora_sft.yaml

model_name_or_path: base model path
adapter_name_or_path: finetuned adapter path
template: qwen
trust_remote_code: true

export_dir: ../dataflex_saves
export_size: 5
export_device: cpu
export_legacy_format: false

Run the export command (inside the LLaMA‑Factory directory):

llamafactory-cli export llama3_lora_sft.yaml

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9. Evaluation & Comparison

We recommend using the DataFlow QA evaluation pipeline to compare NEAR against Less and random sampling.