Formula

Transform

Append a new column whose value is the result of evaluating a per-row expression in CEL — Google’s Common Expression Language. Each input row is passed to the expression as the evaluation context, with column names available as variables. Use it to derive computed fields (totals, ratios, formatted strings), conditional flags, or normalized values from existing columns.

Local processing

This transform runs entirely in your browser. No data is sent to external servers.

How it works

Formula is a streaming transform: each input row is evaluated independently and emitted with one extra column appended. CEL expressions are parsed once when the transform starts and reused per row, so per-row evaluation is fast even on large inputs.

The CEL flavor used is @marcbachmann/cel-js. The transform additionally registers cross-type arithmetic operators (mixed int and dyn<double>) so that integer literals work naturally with column values that arrive as JavaScript numbers, e.g. Amount * -1 does not require a cast. See apps/web/src/transforms/computed-column/logic.ts:23-38.

If either the expression or the output column name is empty, rows pass through unchanged.

Input: One tabular data connection. Output: The same columns plus the new computed column appended at the right.

Options

Option	Type	Description
expression	string	CEL expression evaluated once per row. Required to compute a value.
outputColumn	string	Name of the column to append. If a column with this name exists, it is overwritten. Required to compute a value.

Both default to empty string. With either empty, the transform is a passthrough.

Referring to columns

Inside the expression, columns are available as bare identifiers. Examples: price, status, signup_year.

For columns whose names contain spaces, hyphens, or other non-identifier characters, use FileBender’s bracket-syntax: [Column Name]. The transform rewrites bracketed references to internal safe identifiers before parsing, so [First Name] + " " + [Last Name] works. See apps/web/src/transforms/computed-column/logic.ts:42-64.

The bracket-syntax is a FileBender extension, not part of CEL. It runs as a preprocessor before the expression is parsed.

Examples

Compute a total from quantity and price

You have an order line items table and want a total column derived from quantity * price.

Before:

product	quantity	price
Widget	3	10
Gadget	1	25
Doohickey	5	4

Configuration: expression: quantity * price, output column: total.

After:

product	quantity	price	total
Widget	3	10	30
Gadget	1	25	25
Doohickey	5	4	20

Concatenate columns with bracket syntax

The source table has column names with spaces. You want a full_name column built from them.

Before:

First Name	Last Name	email
Alice	Anderson	[email protected]
Bob	Brown	[email protected]
Carol	Chen	[email protected]

Configuration: expression: [First Name] + " " + [Last Name], output column: full_name.

After:

First Name	Last Name	email	full_name
Alice	Anderson	[email protected]	Alice Anderson
Bob	Brown	[email protected]	Bob Brown
Carol	Chen	[email protected]	Carol Chen

Conditional flag with a CEL ternary

You want a flagged column that is true when amount exceeds 1000, otherwise false.

Before:

customer	amount
Acme Corp	250
Beta Inc	1500
Gamma LLC	800
Delta Co	3000

Configuration: expression: amount > 1000 ? true : false, output column: flagged.

After:

customer	amount	flagged
Acme Corp	250	false
Beta Inc	1500	true
Gamma LLC	800	false
Delta Co	3000	true

Tips and Edge Cases

• The bracket syntax is a FileBender extension, not part of CEL. It is a textual preprocessor: every [Column Name] token is replaced with a safe internal identifier before the expression is handed to the CEL parser. Nested brackets and dynamic column-name strings are not supported. Mixing styles is fine: price * [Tax Rate] works. See apps/web/src/transforms/computed-column/logic.ts:42-64.
• Per-row evaluation errors drop the offending row. When CEL evaluation throws for a row (e.g. dividing by zero, accessing a column that doesn’t exist on that specific row), the transform yields an error result for that row. Downstream transforms see the row as missing rather than as null. See apps/web/src/transforms/computed-column/logic.ts:137-143.
• A bad expression silently drops every row. If the CEL expression itself fails to parse, every row through the transform yields an error result, so downstream transforms receive nothing. The configuration UI surfaces the parse error, but if the flow auto-runs from a saved config that no longer parses (e.g. a referenced column was renamed upstream), the flow will appear to drop all rows. See apps/web/src/transforms/computed-column/logic.ts:95-112.

Related Transforms

• Add Column — append a static value (no expression).
• Replace Values — rewrite values in an existing column rather than appending a new one.
• Change Type — convert strings to numbers / booleans / dates before using them in arithmetic.
• CEL Expression Language — full syntax reference for operators, built-in functions, and column reference styles.