r - Rstudio auto-completion, undefined options for data columns -

with rstudio, let's create data frame called data.

data = data.frame(a=rep(0,100),b=rep(1,100))    

then, if input data$ , click tab auto-completion, shows options as: a , b (column names defined in data expected) can choose from.

but if input data$ within function, input unique(data$ , click tab, shows options as: germancredit, cars, dhfr,... (which not expected. don't know from.)

in global environment, there no such data germancredit or cars.

if create data using different name say

data2 = data.frame(a=rep(0,100),b=rep(1,100)) 

then, don't trouble.

q: wondering going on here , how can address issue once click on tab, show columns defined in data.

just in case, have installed following packages in rstudio:

grid      stats     graphics  grdevices utils     datasets  methods  base       pryr_0.1.2       e1071_1.6-7      caret_6.0-52     gridextra_2.0.0   boot_1.3-17      lmtest_0.9-34    zoo_1.7-12       paireddata_1.0.1  ggplot2_1.0.1    lattice_0.20-33  mvtnorm_1.0-3    gld_2.3.1        mass_7.3-43 

thank reading.