I want to vertically merge two polars.LazyFrames in order to avoid collecting both LazyFrames beforehand, which is computationally expensive. I have tried extend(), concat(), and vstack() but none of them are implemented for LazyFrames. Maybe I am missing the point about LazyFrames by trying to perform this operation, but I am aware that join() works, which would also alter the dataframe's structure.

I want to vertically merge two polars.LazyFrames in order to avoid collecting both LazyFrames beforehand, which is computationally expensive. I have tried extend(), concat(), and vstack() but none of them are implemented for LazyFrames. Maybe I am missing the point about LazyFrames by trying to perform this operation, but I am aware that join() works, which would also alter the dataframe's structure.

• python
• dataframe
• python-polars
• polars

Share Improve this question Follow edited Mar 10 at 17:14 cafce25 28k55 gold badges4545 silver badges5858 bronze badges asked Mar 10 at 16:28 realbitsurferrealbitsurfer 7677 bronze badges 1

• My bad, I did not read the error message of my concat() attempt close enough. Thank you for the answer! – realbitsurfer Commented Mar 12 at 16:41

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1 Answer 1

Sorted by: Reset to default 8

pl.concat can be used with LazyFrames:

>>> lf = pl.LazyFrame({"x": [1, 2]})
>>> pl.concat([lf, lf]).collect()
shape: (4, 1)
┌─────┐
│ x   │
│ --- │
│ i64 │
╞═════╡
│ 1   │
│ 2   │
│ 1   │
│ 2   │
└─────┘