# Create some sample data.
dates <- seq(as.Date("2015/5/1"), as.Date("2015/6/30"), length.out=100)
values <- sample(1:100, length(dates))

# Create a data.frame of data.
data <- data.frame(Date = dates, Value = values)

# Split by day.
dataByDay <- split(data, data$Date)

# Get list of data counts and sum per day.
# Method 1.
dataCountsByDay1 <- data.frame()
x <- sapply(dataByDay, function(r) {
  df <- data.frame(r)
  row <- data.frame(Count = nrow(df), Total = sum(df$Value), Date = df[1,]$Date)
  dataCountsByDay1 <<- rbind(dataCountsByDay1, row)
})

# Get list of data counts and sum per day.
# Method 2.
dataCountsByDay2 <- as.data.frame(t(sapply(dataByDay, function(r) {
  df <- data.frame(r)
  c(Count = nrow(df), Total = sum(df$Value))
})))
dataCountsByDay2$Date <- as.Date(row.names(dataCountsByDay2))

# Verify they're both equivalent.
dataCountsByDay1$Count == dataCountsByDay2$Count
dataCountsByDay1$Total == dataCountsByDay2$Total
as.character(dataCountsByDay1$Date) == as.character(dataCountsByDay2$Date)
nrow(dataCountsByDay1) == nrow(dataCountsByDay2)