[R] contraints in ltm package

Hello all, I have a brief IRT related question regarding the ltm package. I am am using tpm which is part of the ltm package. I am constraining the item parameters for this package since they have been estimated earlier. I notice that the difficulty parameter changes, despite the fact that it is

[R] odd behavior of data.matrix()

Hi R community, I have been trying to figure out why R is reversing the order of rows after I run data.matrix() Here is my data: df<-structure(list(itmID = c(1L, 2L, 1L, 2L, 1L, 2L), variable = structure(c(1L, 1L, 2L, 2L, 3L, 3L), .Label = c("3", "2", "1"), class = "factor"), value = c(0.7,

[R] testEquatingData (part of ltm package) changes order of columns

Dear R community, I hope someone is out there who has some insights into the ltm package. Specifically, I am seeking help for the testEquatingData function which is part of this package. Here is an example of my data: #install.packages("ltm", dependencies = TRUE) library(ltm) anchor<- as.data.f

Re: [R] adding row ID numbers by group

,10,11,12,13,14,15) > data<-data.frame(group, var2) > data > ddply(data,"group",transform,ID=1:length(group)) > > Felipe D. Carrillo > Supervisory Fishery Biologist > Department of the Interior > US Fish & Wildlife Service > California, USA > > > >

[R] adding row ID numbers by group

Hello R community, I am hoping for some help with the following problem. I have a data frame containing various groups. These groups are identified by a grouping variable. I would like to add a sequential ID number to each group to later sort these individuals within each group by this ID number.

[R] Different colors for different groups in lattice wireframe

Hello, I have trouble with the following: I am trying do display two groups in a wireframe using two different color schemes. I have been able to display the two groups, but the color scheme for both is identical. I would like to display one group in a color scheme red-yellow (or whatever) and the