Use a text field as a way to link to other users profile on BuddyPress

gistfile1.txt

class BP_Other_User_As_Profile_Field {

	/**
	 * Field id, replace with actual field id.
	 *
	 * @var string
	 */
	private $field_id = 25; // Chang it with actual field id.

	/**
	 * BP_Other_User_As_Profile_Field constructor.
	 */
	public function __construct() {
		add_action( 'bp_signup_validate', array( $this, 'validate' ) );
		add_filter( 'bp_get_the_profile_field_value', array( $this, 'filter' ) );
	}

	/**
	 * Validate fields.
	 */
	public function validate() {
		if ( ! bp_is_active( 'xprofile' ) ) {
			return;
		}

		$profile_field_ids = isset( $_POST['signup_profile_field_ids'] ) ? explode( ',', $_POST['signup_profile_field_ids'] ) : array();

		if ( ! in_array( $this->field_id, $profile_field_ids ) ) {
			return;// no need to validate, the field is not available on signup page.
		}

		if ( empty( $_POST[ 'field_' . $this->field_id ] ) ) {
			return;// if it is required, bp will take care.
		}

		$email = trim( $_POST[ 'field_' . $this->field_id ] );
		$user  = get_user_by( 'email', $email );
		if ( ! $user ) {
			buddypress()->signup->errors[ 'field_' . $this->field_id ] = __( 'Please enter a valid email' );
		}
	}

	/**
	 * Filter value to link to user profile.
	 *
	 * @param mixed $value value.
	 *
	 * @return mixed|string
	 */
	public function filter( $value ) {
		global $field;

		if ( $this->field_id != $field->id || empty( $value ) ) {
			return $value;
		}


		$user = get_user_by( 'email', $value );
		if ( ! $user ) {
			return 'N/A'; //invalid user.
		}

		return bp_core_get_userlink( $user->ID );
	}
}

new BP_Other_User_As_Profile_Field();