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:
Ozone Solar.R Wind Temp
Min. : 1.00 Min. : 7.0 Min. : 1.700 Min. :56.00
1st Qu.: 18.00 1st Qu.:115.8 1st Qu.: 7.400 1st Qu.:72.00
Median : 31.50 Median :205.0 Median : 9.700 Median :79.00
Mean : 42.13 Mean :185.9 Mean : 9.958 Mean :77.88
3rd Qu.: 63.25 3rd Qu.:258.8 3rd Qu.:11.500 3rd Qu.:85.00
Max. :168.00 Max. :334.0 Max. :20.700 Max. :97.00
NA's :37 NA's :7
Month Day
Min. :5.000 Min. : 1.0
1st Qu.:6.000 1st Qu.: 8.0
Median :7.000 Median :16.0
Mean :6.993 Mean :15.8
3rd Qu.:8.000 3rd Qu.:23.0
Max. :9.000 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:
The summary of each variable is
Ozone: Min. 1 1st Qu. 18 Median 31.5 Mean 42.1293103448276 3rd Qu. 63.25 Max. 168 NA's 37
Solar.R: Min. 7 1st Qu. 115.75 Median 205 Mean 185.931506849315 3rd Qu. 258.75 Max. 334 NA's 7
Wind: Min. 1.7 1st Qu. 7.4 Median 9.7 Mean 9.95751633986928 3rd Qu. 11.5 Max. 20.7
Temp: Min. 56 1st Qu. 72 Median 79 Mean 77.8823529411765 3rd Qu. 85 Max. 97
Month: Min. 5 1st Qu. 6 Median 7 Mean 6.99346405228758 3rd Qu. 8 Max. 9
Day: Min. 1 1st Qu. 8 Median 16 Mean 15.8039215686275 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.