Source

File: wp-includes/wp-db.php

protected function process_field_formats( $data, $format ) {
		$formats          = (array) $format;
		$original_formats = $formats;

		foreach ( $data as $field => $value ) {
			$value = array(
				'value'  => $value,
				'format' => '%s',
			);

			if ( ! empty( $format ) ) {
				$value['format'] = array_shift( $formats );
				if ( ! $value['format'] ) {
					$value['format'] = reset( $original_formats );
				}
			} elseif ( isset( $this->field_types[ $field ] ) ) {
				$value['format'] = $this->field_types[ $field ];
			}

			$data[ $field ] = $value;
		}

		return $data;
	}