Parsing a String with DO Statements

This function parses a string and expands this string in case of DO statements which are shortcuts for writing loops. The statement DO(n,m,k) increments an index from n to m in steps of k. The index in the string model must be defined as %. For a nested loop within a loop, the DO2 statement can be used using %1 and %2 as indices. See Examples for hints on the specification. The loop in DO2 must not be explicitly crossed, e.g. in applications for specifying covariances or correlations. The formal syntax for
for (ii in 1:(K-1)){ for (jj in (ii+1):K) { ... } }
can be written as DO2(1,K-1,1,%1,K,1 ). See Example 2.

doparse(model)

Arguments

model

A string with DO or DO2 statements.

Value

Parsed string in which DO statements are expanded.

See also

This function is also used in lavaanify.IRT and tamaanify.

Examples

#############################################################################
# EXAMPLE 1: doparse example
#############################################################################

# define model
model <- "
 # items I1,...,I10 load on G
 DO(1,10,1)
   G=~ lamg% * I%
 DOEND
 I2 | 0.75*t1
 v10 > 0 ;
 # The first index loops from 1 to 3 and the second index loops from 1 to 2
 DO2(1,3,1,  1,2,1)
   F%2=~ a%2%1 * A%2%1 ;
 DOEND
 # Loop from 1 to 9 with steps of 2
 DO(1,9,2)
   HA1=~ I%
   I% | beta% * t1
 DOEND
 "

# process string
out <- TAM::doparse(model)
cat(out)
  ##    # items I1,...,I10 load on G
  ##       G=~ lamg1 * I1
  ##       G=~ lamg2 * I2
  ##       G=~ lamg3 * I3
  ##       G=~ lamg4 * I4
  ##       G=~ lamg5 * I5
  ##       G=~ lamg6 * I6
  ##       G=~ lamg7 * I7
  ##       G=~ lamg8 * I8
  ##       G=~ lamg9 * I9
  ##       G=~ lamg10 * I10
  ##     I2 | 0.75*t1
  ##     v10 > 0
  ##       F1=~ a11 * A11
  ##       F2=~ a21 * A21
  ##       F1=~ a12 * A12
  ##       F2=~ a22 * A22
  ##       F1=~ a13 * A13
  ##       F2=~ a23 * A23
  ##       HA1=~ I1
  ##       HA1=~ I3
  ##       HA1=~ I5
  ##       HA1=~ I7
  ##       HA1=~ I9
  ##       I1 | beta1 * t1
  ##       I3 | beta3 * t1
  ##       I5 | beta5 * t1
  ##       I7 | beta7 * t1
  ##       I9 | beta9 * t1

#############################################################################
# EXAMPLE 2: doparse with nested loop example
#############################################################################

# define model
model <- "
 DO(1,4,1)
   G=~ lamg% * I%
 DOEND
 # specify some correlated residuals
 DO2(1,3,1,%1,4,1)
   I%1 ~~ I%2
 DOEND
 "
# process string
out <- TAM::doparse(model)
cat(out)
  ##       G=~ lamg1 * I1
  ##       G=~ lamg2 * I2
  ##       G=~ lamg3 * I3
  ##       G=~ lamg4 * I4
  ##     # specify some correlated residuals
  ##       I1 ~~ I2
  ##       I1 ~~ I3
  ##       I1 ~~ I4
  ##       I2 ~~ I3
  ##       I2 ~~ I4
  ##       I3 ~~ I4