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Dask Cheat Sheet

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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