/**
 * Checks if given string is URL.
 */
export declare const isURL: (filepath: string) => boolean;
/**
 * Checks if given `filepath` is url, then tries to fetch it.
 * Otherwise tries to read file.
 */
export declare const retrieveFile: (filepath: string) => Promise<any>;
/**
 * Checks if value is invalid: `undefined`, `null` or an empty string, then sets `nan` instead.
 */
export declare const setNanValue: (value: any) => any;
/**
 * Converts empty values to `nan`.
 */
export declare const nanifyEmptyValues: (object: any) => any;
/**
 * If `field` is missing from `object`, then reject with error.
 * Otherwise nanify empty values and return data.
 */
export declare const fieldAccessor: (field: string, object: any) => any;
/**
 * Parses CSV file.
 */
export declare const parseCSVFile: (file: string | Buffer) => any[];