The standard presentation of a summary of a data frame where each variable is given its own column is difficult for a screen reader user to read as the processing of information is done line by line. For example:
summary(airquality) Ozone Solar.R Wind Temp
Min. : 1.0 Min. : 7 Min. : 1.70 Min. :56.0
1st Qu.: 18.0 1st Qu.:116 1st Qu.: 7.40 1st Qu.:72.0
Median : 31.5 Median :205 Median : 9.70 Median :79.0
Mean : 42.1 Mean :186 Mean : 9.96 Mean :77.9
3rd Qu.: 63.2 3rd Qu.:259 3rd Qu.:11.50 3rd Qu.:85.0
Max. :168.0 Max. :334 Max. :20.70 Max. :97.0
NA's :37 NA's :7
Month Day
Min. :5.00 Min. : 1.0
1st Qu.:6.00 1st Qu.: 8.0
Median :7.00 Median :16.0
Mean :6.99 Mean :15.8
3rd Qu.:8.00 3rd Qu.:23.0
Max. :9.00 Max. :31.0
The VI() command actually calls the VI.data.frame() command. It then processes each variable one by one so that the results are printed variable by variable instead of summary statistic by summary statistic. For example:
VI(airquality)
The summary of each variable is
Ozone: Min. 1 1st Qu. 18 Median 31.5 Mean 42.1 3rd Qu. 63.2 Max. 168 NA's 37
Solar.R: Min. 7 1st Qu. 116 Median 205 Mean 186 3rd Qu. 259 Max. 334 NA's 7
Wind: Min. 1.7 1st Qu. 7.4 Median 9.7 Mean 9.96 3rd Qu. 11.5 Max. 20.7
Temp: Min. 56 1st Qu. 72 Median 79 Mean 77.9 3rd Qu. 85 Max. 97
Month: Min. 5 1st Qu. 6 Median 7 Mean 6.99 3rd Qu. 8 Max. 9
Day: Min. 1 1st Qu. 8 Median 16 Mean 15.8 3rd Qu. 23 Max. 31 Note that in this case, the blind student could choose to present the summary of each variable as generated by the VI() command, or the output from the standard summary() command. There is no difference in the information that is ultimately presented in this case.