/**
 * Calculates the daily returns for a given array of data objects.
 *
 * The function computes the daily return for each row based on the specified `sourceColumn`.
 * The daily return is calculated as `(current - previous) / previous` for each consecutive row.
 * The result is stored in a new column specified by `resultColumn` (default: `'dailyReturn'`).
 * The first row's daily return is set to `initialValue` (default: `0`).
 * If the required values are not valid numbers or the previous value is zero, the daily return is set to `null`.
 *
 * @param data - Array of data objects containing the source values.
 * @param sourceColumn - The key in each object from which to read the value for return calculation.
 * @param resultColumn - The key under which to store the calculated daily return (default: `'dailyReturn'`).
 * @param initialValue - The value to assign as the daily return for the first row (default: `0`).
 * @returns A new array of data objects with the daily returns added in the specified result column.
 */
export declare function calculateDailyReturns(data: Array<Record<string, unknown>>, sourceColumn: string, resultColumn?: string, initialValue?: number | null): Array<Record<string, unknown>>;
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