nwsIFindTry               package:nws               R Documentation

_n_e_t_W_o_r_k_S_p_a_c_e _C_l_a_s_s _M_e_t_h_o_d

_D_e_s_c_r_i_p_t_i_o_n:

     Create a function that acts as a non-destructive iterator over the
     values of the specified variable.

_U_s_a_g_e:

     ## S4 method for signature 'netWorkSpace':
     nwsIFindTry(.Object, xName, defaultVal=NULL)

_A_r_g_u_m_e_n_t_s:

 .Object: a netWorkSpace class object

   xName: name of the variable to be fetched

defaultVal: value to return, if xName is not found in the netWorkSpace

_D_e_t_a_i_l_s:

     The iterator function returned by the nwsIFindTry method takes no
     arguments, and works somewhat like the nwsFindTry method,
     specified with the same arguments that were passed to nwsIFindTry.
     The difference is that the nwsFindTry method cannot iterate
     through the values of a variable; it always returns the same value
     until the variable is modified. The iterator function, however,
     maintains some state that allows it to see subsequent values. Each
     time the iterator function is called, it returns the next value in
     the variable. Once all values in the variable have been returned,
     the iterator function will return defaultVal. However, when new
     values are stored into the variable, the iterator function will
     return them, picking right up where it left off.

_S_e_e _A_l_s_o:

     'nwsFindTry', 'nwsIFind'

_E_x_a_m_p_l_e_s:

     ## Not run: 
     ws <- netWorkSpace('nws example')
     nwsStore(ws, 'x', 1)
     nwsStore(ws, 'x', 2)
     it <- nwsIFindTry(ws, 'x', NA)
     it()  # returns the value 1
     it()  # returns the value 2
     it()  # returns the value NA
     nwsStore(ws, 'x', 3)
     it()  # returns the value 3
     it()  # returns the value NA
     ## End(Not run)

