Character columns in a data table can use significant space in memory and on disk. Compact character columns reduce memory usage by only storing each distinct value in a character column once. Compact character columns can be enabled in preferences or through the Column Info window.
To enable compact character columns
1. Select File > Preferences and click General.
2. Select the Open character columns as compact columns option.
3. Select the New character columns default to compact option.
4. Click OK to return to the data table.
The columns that receive the largest performance benefit from compact character columns have low proportions of distinct values. For instance, a column of the names of students where almost every value is unique will receive fewer benefits than a column of “yes” and “no” answers to a survey.
A table saved with file compression can use significantly less space than one saved without it. Compact character columns can be used in place of or in conjunction with file compression for a variety of benefits.
While file compression can save disk space, it comes at the cost of performance. An uncompressed data table will load and save much faster than when file compression is used.
Because a data table that uses compact character columns will usually be much smaller than an identical data table that uses normal character columns, compact character columns give the performance benefits of uncompressed files while saving disk space and memory usage.
For users whose primary concern is saving memory, using file compression in addition to compact character columns can provide significant benefits.
Compact character columns are not compatible with JMP 17 and earlier.