Kelsey - 1 year ago 70
R Question

# Extract First and Last date from one column and Insert into 2 new columns

I have a dataset of water quality data with Date, Result, Parameter, Station in R. I am trying to extract the first and last date that a sample was taken PER station which would take up two new columns at the end of my dataframe. I also have columns for Month, Day, and Year.

Here is the structure:

``````'data.frame':   50954 obs. of  8 variables:
\$ Date     : chr  "6/9/2016" "6/9/2016" "6/8/2016" "6/8/2016" ...
\$ Result   : num  400 160 2200 260 660 550 2100 270 750 82 ...
\$ Units    : chr  "M" "M" "M" "M" ...
"Fecal coliforms" ...
\$ Station  : chr  "RIO GRANDE DE MANATI AT HWY 2 NR MANATI, PR" "RIO GRANDEE DE MANATI AT HWY 2 NR MANATI, PR" "RIO CAONILLAS NR JAYUYA, PR"
"RIO CAONILLAS NR JAYUYA, PR" ...
\$ month    : num  6 6 6 6 6 6 6 6 6 6 ...
\$ year     : num  2016 2016 2016 2016 2016 ...
\$ day      : num  9 9 8 8 8 8 7 7 7 7 ...
``````

I've been doing this to extract summary statistics by station:

``````P303.split <- split(P303, Parameter)
Copper = P303.split\$'Copper'
CopperSumStats = data.frame(do.call("rbind", by(Copper[, "Result"],  Copper[,"Station"], summary)))
``````

So now just need start and end dates... Thanks in advance!

I think you could use `dplyr` to perform the calculations you need:

``````library(dplyr) #load package
df1\$Date <- as.Date(df1\$Date, format = "%d/%m/%Y") #format date
#data manipulation
df1 %>%
group_by(Station) %>%
mutate(FirstDate = min(Date), LastDate = max(Date)) -> df2
``````

This solution assumes your data is in a `data.frame` named `df1`.

Recommended from our users: Dynamic Network Monitoring from WhatsUp Gold from IPSwitch. Free Download