Data Frame, wrong summary

Question 1

It's a rounding problem. All the output from summary(FTSE$LastPrice) has only 4 significant digits. If you look at ?summary in its Usage section you see the default for digits (as a named argument) coupled with the default for digits as an option gets your to 4.

 # summary(object, ..., digits = max(3, getOption("digits")-3))

> getOption("digits")
[1] 7

So try:

summary(FTSE$LastPrice, digits=7)

An unanswered question remains, however: Why does the summary.data.frame function not do the same degree of rounding, since the default argument to digits is the same for the .default and the .data.frame methods? Looking at the code you see that summary.data.frame actually first does summary.default on its columns with a fixed value of digits=12L, and later uses the digits argument to format. It seemed to me that the help page was somewhat obscure in this area in it arguments description

digits: integer, used for number formatting with signif() (for summary.default) or 
                                                 format() (for  summary.data.frame).

It completely ignores the fact that the default (and fixed) signif for data.frame columns is quite different.

Question 2

The method for summary on data.frame is different then the default method for a vector. Probably resulting in using a different precision for computation. Read more here. If you explicitly specify digits, it works:

Lets create the data:

nr <- 21167
set.seed(nr)
temp <- data.frame(Name=sample(c("FTSE","FTSE NET"),nr,replace=T),
                   DateLastTrade=sample(1:18,nr,replace=T),
                   LastPrice = sample(18000:21000,nr,replace=T),
                   Open = 19091,
                   LastClose = 19021
                   )


str(temp)

Now lets reproduce what you got:

summary(temp)
summary(temp$LastPrice)

Now lets fix that:

summary(temp,digits=7)
summary(temp$LastPrice,digits=7)

Note: This will only work if your numbers are <10^7-1, i.e. if they have <= 7 digits. You'll not see the effect at 10^7, but if 10^7+1 is there, then the last digit will be rounded down to zero. To solve that you'll have to increase digits to 8 (and so on). It is safer to use a larger value, e.g. digit=10