Dask Cheat Sheet
Dask reference covering parallel DataFrame and Array APIs, delayed task graphs, lazy evaluation, and the distributed scheduler client.
2 PagesIntermediateMar 28, 2026
Dask DataFrame
Pandas-like API that scales out of core.
python
import dask.dataframe as dddf = dd.read_csv("data-*.csv") # reads many files as one logical DataFrameresult = df.groupby("category")["value"].mean()computed = result.compute() # triggers actual executiondf["ratio"] = df["a"] / df["b"] # lazy, builds a task graphdf.to_parquet("output/", engine="pyarrow")
Dask Array & Delayed
Parallelize NumPy-style code and arbitrary functions.
python
import daskfrom dask import delayedimport dask.array as dax = da.random.random((10000, 10000), chunks=(1000, 1000))y = (x + x.T).mean(axis=0)result = y.compute()@delayeddef process(x): return x * 2tasks = [process(i) for i in range(10)]results = dask.compute(*tasks)
Distributed Client
Run tasks on a local or remote cluster.
python
from dask.distributed import Clientclient = Client(n_workers=4, threads_per_worker=2) # local clusterprint(client.dashboard_link) # web UI for the task graphfuture = client.submit(process, 10)result = future.result()client.close()
Core Concepts
Fundamental Dask building blocks.
- dask.dataframe- parallel pandas-like API for larger-than-memory tables
- dask.array- parallel NumPy-like API for chunked arrays
- dask.delayed- wraps arbitrary Python functions into lazy task graphs
- .compute()- triggers execution and returns a concrete result
- Client- connects to a local or distributed scheduler with a diagnostics dashboard
- chunks / partitions- controls parallelism granularity for arrays/dataframes
Pro Tip
Dask operations are lazy by default — build up your full pipeline of transformations first, then call .compute() once at the end so Dask can optimize and parallelize the whole task graph instead of materializing intermediate results.
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