skip over rows in pretraining dataset (#2223)

* skip over rows in pretraining dataset

* update docs

docs/dataset-formats/pretraining.qmd

@@ -19,7 +19,14 @@ For pretraining, there is no prompt template or roles.  The only required field
 Axolotl usually loads the entire dataset into memory. This will be challenging for large datasets. Use the following config to enable streaming:
 
 ```{.yaml filename="config.yaml"}
-pretraining_dataset: # hf path only
+pretraining_dataset:
+  - name:
+    path:
+    split:
+    text_column: # column in dataset with the data, usually `text`
+    type: pretrain
+    trust_remote_code:
+    skip: # number of rows of data to skip over from the beginning
 ...
 ```
 

src/axolotl/utils/config/models/input/v0_4_1/__init__.py

@@ -129,6 +129,7 @@ class PretrainingDataset(BaseModel):
     type: Optional[str] = "pretrain"
     trust_remote_code: Optional[bool] = False
     data_files: Optional[str] = None
+    skip: Optional[int] = None
 
 
 class UserDefinedPrompterType(BaseModel):

src/axolotl/utils/data/sft.py

@@ -89,11 +89,13 @@ def prepare_dataset(cfg, tokenizer, processor=None):
         split = "train"
         name = None
         data_files = None
+        skip = 0
         if isinstance(cfg.pretraining_dataset, list) and isinstance(
             cfg.pretraining_dataset[0], dict
         ):
             path = cfg.pretraining_dataset[0]["path"]
             name = cfg.pretraining_dataset[0]["name"]
+            skip = cfg.pretraining_dataset[0]["skip"]
             if "split" in cfg.pretraining_dataset[0]:
                 split = cfg.pretraining_dataset[0]["split"]
 
@@ -107,10 +109,12 @@ def prepare_dataset(cfg, tokenizer, processor=None):
             cfg.pretraining_dataset[0]["type"] or "pretrain",
         )
 
+        iter_ds = load_dataset(path, streaming=True, split=split, name=name, data_files=data_files)
+        if skip:
+            LOG.info(f"Skipping {skip} samples from the dataset")
+            iter_ds = iter_ds.skip(skip)
         train_dataset = wrap_pretraining_dataset(
-            load_dataset(
-                path, streaming=True, split=split, name=name, data_files=data_files
-            ),
+            iter_ds,
             tokenizer,
             cfg,
             ds_wrapper_partial,