Are there any good R object browsers?

Question

S-Plus has a great object explorer and data editor built into its GUI. It allows you to easily see all the objects in the workspace at a glance, and sort them by name, size

Answer 1

str() is very useful. Specifying give.attr=FALSE hides attributes.

> str(diamonds)
'data.frame':   53940 obs. of  10 variables:
 $ carat  : num  0.23 0.21 0.23 0.29 0.31 0.24 0.24 0.26 0.22 0.23 ...
 $ cut    : Factor w/ 5 levels "Fair","Good",..: 5 4 2 4 2 3 3 3 1 3 ...
 $ color  : Factor w/ 7 levels "D","E","F","G",..: 2 2 2 6 7 7 6 5 2 5 ...
 $ clarity: Factor w/ 8 levels "I1","SI2","SI1",..: 2 3 5 4 2 6 7 3 4 5 ...
 $ depth  : num  61.5 59.8 56.9 62.4 63.3 62.8 62.3 61.9 65.1 59.4 ...
 $ table  : num  55 61 65 58 58 57 57 55 61 61 ...
 $ price  : int  326 326 327 334 335 336 336 337 337 338 ...
 $ x      : num  3.95 3.89 4.05 4.2 4.34 3.94 3.95 4.07 3.87 4 ...
 $ y      : num  3.98 3.84 4.07 4.23 4.35 3.96 3.98 4.11 3.78 4.05 ...
 $ z      : num  2.43 2.31 2.31 2.63 2.75 2.48 2.47 2.53 2.49 2.39 ...