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I am relatively new to R I have a large data set which gives several data values for that day. So to simplify matters I need to get an average value for each day in in one table displaying the day and the average value. 

Date_Recorded     Value
2016-08-19        74.2
2016-08-19        74.6
2016-08-20        85.63
2016-08-20        88.55

And I would like the resulting table to look like this 

Date_Recorded     Value
2016-08-19        74.4
2016-08-20        87.09

Then after this How would I go about pulling out a date range of data say from 2016-08-20 to 2018-02-04 out of this data set or any other dataset?

Island868
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    To aggregate, use... well, `aggregate()` - see [here for more info](https://stackoverflow.com/questions/6289538/aggregate-a-dataframe-on-a-given-column-and-display-another-column). For your second part, make sure your `Date_Recorded` variable is set as datetime and simply do `df[df$Date_Recorded >= ... & df$Date_Recorded <= ..., ]` – Sotos Oct 02 '18 at 14:26

2 Answers2

1

Great answer by Chabo. Alternatively, you could use the tidyverse approach:

library(tidyverse)

Date_Recorded<-c("2016-08-19", "2016-08-19", "2016-08-20", 
                 "2016-08-20", "2016-08-21", "2016-08-21")

Value <- c(74.2, 74.6, 85.63, 
           88.55, 70.1, 70.2)

df<-data.frame(Date_Recorded,Value)

df$Date_Recorded<-as.Date(df$Date_Recorded)

# To create the resulting table you wanted
df %>%
  group_by(Date_Recorded) %>% 
  summarise(mean(Value, na.rm = FALSE))


# Or to search for a date range. You could use filter(Date_Recorded == "2018-10-02") to 
# serach for a single date
df %>%
  filter(Date_Recorded >= "2016-08-20" & Date_Recorded <= "2016-08-21") %>% #to select a date range
  group_by(Date_Recorded) %>%
  summarise(mean(Value, na.rm = FALSE))
Andrew
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0

We can do this using aggregate, part of the base statistics in R...

Date_Recorded<-c(  
"2016-08-19",        
"2016-08-19",        
"2016-08-20",      
"2016-08-20")

Value<-c(
74.2,
74.6,
85.63,
88.55
)

df<-data.frame(Date_Recorded,Value)

df$Date_Recorded<-as.Date(df$Date_Recorded)

test_df<-aggregate(df["Value"], by=df["Date_Recorded"], FUN=mean)

> test_df
  Date_Recorded  Value
1    2016-08-19   74.40
2    2016-08-20   87.09

# As pointed out by @Sotos
start_date<-as.Date("2016-08-18")
end_date<-as.Date("2016-08-19")

test_df[test_df$Date_Recorded >= start_date & test_df$Date_Recorded <= 
end_date, ]

  Date_Recorded Value
1    2016-08-19  74.4

Credit to @Sotos for the second half of this question.

Chabo
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  • Thank you. That worked... however how would I go about pulling out a date range of data say from 2016-08-20 to 2018-02-04 out of this data set or any other dataset? – Island868 Oct 02 '18 at 14:44
  • Please see the new edits, as pointed out by @Sotos we can apply a subset to our data. – Chabo Oct 02 '18 at 14:45