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| Expression$scalar(x) constructs an Expression which always evaluates to |
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| Expression$scalar(x) constructs an Expression which always evaluates to |
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| <h1>Arrow expressions</h1> |
| <small class="dont-index">Source: <a href="https://github.com/apache/arrow/blob/main/r/R/expression.R" class="external-link"><code>R/expression.R</code></a></small> |
| <div class="d-none name"><code>Expression.Rd</code></div> |
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| <div class="ref-description section level2"> |
| <p><code>Expression</code>s are used to define filter logic for passing to a <a href="Dataset.html">Dataset</a> |
| <a href="Scanner.html">Scanner</a>.</p> |
| <p><code>Expression$scalar(x)</code> constructs an <code>Expression</code> which always evaluates to |
| the provided scalar (length-1) R value.</p> |
| <p><code>Expression$field_ref(name)</code> is used to construct an <code>Expression</code> which |
| evaluates to the named column in the <code>Dataset</code> against which it is evaluated.</p> |
| <p><code>Expression$create(function_name, ..., options)</code> builds a function-call |
| <code>Expression</code> containing one or more <code>Expression</code>s. Anything in <code>...</code> that |
| is not already an expression will be wrapped in <code>Expression$scalar()</code>.</p> |
| <p><code>Expression$op(FUN, ...)</code> is for logical and arithmetic operators. Scalar |
| inputs in <code>...</code> will be attempted to be cast to the common type of the |
| <code>Expression</code>s in the call so that the types of the columns in the <code>Dataset</code> |
| are preserved and not unnecessarily upcast, which may be expensive.</p> |
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