Assign and Print

Feb 23, 20252 min read

just stumbled upon this neat little R pattern which I found really nice/helpful. I was assigning and evaluating some expressions, but I also wanted to see what values I was getting. Toy example:

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set.seed(0)
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x <- runif(10)
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x
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#>  [1] 0.8966972 0.2655087 0.3721239 0.5728534 0.9082078 0.2016819 0.8983897
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#>  [8] 0.9446753 0.6607978 0.6291140
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xbar <- mean(x)
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xbar
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#> [1] 0.635005

I was working in a script, so I was just mashing Ctr + Enter a few times to run the above snippet. Obviously in a notebook such a command could be condensed to just the chord for Run Cell, but my point will stand.

You can rewrite the above like this:

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set.seed(0)
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x <- runif(10)
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print(x)
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#>  [1] 0.8966972 0.2655087 0.3721239 0.5728534 0.9082078 0.2016819 0.8983897
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#>  [8] 0.9446753 0.6607978 0.6291140
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xbar <- mean(x)
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print(xbar)
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#> [1] 0.635005

but this is unnecessary since evaluating x will print it. I was thinking about this when I remembered that print returns invisibly⁠. This allows you to condense above to just:

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set.seed(0)
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x <- runif(10) |> print()
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#>  [1] 0.8966972 0.2655087 0.3721239 0.5728534 0.9082078 0.2016819 0.8983897
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#>  [8] 0.9446753 0.6607978 0.6291140
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xbar <- mean(x) |> print()
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#> [1] 0.635005

I think this looks a lot nicer.

I popped it into a small snippet as well, just for kicks.

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{
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    "Evaluate and Print": {
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    "prefix": "eprint",
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    "body": "|> print()",
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    "description": "Piped input gets printed and returned invisibly; useful for printing an expression and assigning it."
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  }
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}

All R snippets above created on 2025-02-23 with reprex v2.1.1⁠

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Dixi.@visruth.com