# Concatenating alignments

The `concat` app provides a mechanism to concatenate alignments.

Let’s create sample alignments with matching sequence names to use in the below examples.

## How to concatenate alignments

By default, sequences without matching names in the corresponding alignment are omitted (`intersect=True`).

## How to concatenate alignments with missing sequences

By providing the argument `intersect=False`, the `concat` app will include missing sequences across alignments. Missing sequences are replaced by a sequence of `"?"`.

## How to concatenated alignments with a delimiter `"N"`

You can insert an `"N"` character in between the concatenated sequences.

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Select n sequences from a collection

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Writing Data