search for: r0000160

I have a data frame where I need to subset certain rows before I compute the mean of another variable. However, the value that I need to subset by is found in multiple columns. For example, in the data below the value R0000160 is found in the first and second columns (itd_1 and itd_45). These data are student responses to multiple choice test items from a computer adaptive test. So, the variable itd_1 denotes that item i was presented to student k in position t and then the variable righta_a and righta_b denotes a corre...