[R] Getting minimum value of a column according a factor column of a dataframe

[javad bayat]

;Dear all
First of all I appreciate you for the answers you have sent. I did the
codes that Rui provided and I got what I wanted.
"
res <- lapply(split(df1, df1$Code), \(x) x[which.min(x$Q),])
res <- do.call(rbind, res)
i <- order(unique(df1$Code))
res[order(i), ]
"
I think I should explain more about my request. I had a large data frame
(11059 rows and 16 columns). The Code column represented the stations code,
totally the number of stations were 128. At each station I had many
measured variables, like Q and N and O, and these variables were measured
in different years and days. The days that data were measured were
different for each station, and due to this reason I had different rows for
stations. For example, station number one (41009) had 158 rows and station
number 2 (41011) had 113 rows. Note that the station's codes are not in
order format (e.g smallest to largest).
Back to my request, I wanted to extract the minimum value of the Q for each
station (based on the Code column). The problem was that I wanted to have
other column values which were measured for this minimum of the Q.
I hope my explanation was clear enough. As I said before, I used the Rui's
codes and I got what I wanted. Although, other solutions provided by others
were all correct.

Regarding my request, unfortunately I faced another problem. I had to
extract the maximum of the Q and put it exactly under the minimum of the Q.
Something like the below one:
"

Code

              Y

              M

               D

           Q

            N

             O

41003

81

1

19

0.16

7.17

2.5

41003

79

8

17

10.21

5.5

7.2

41009

79

2

21

0.218

5.56

4.04
41009 79 10 20 12.24 5.3 7.1
.
.
.
.
"
I extract both min and max according to the codes, and I have 2 dataframes,
one for the minimum values and another for the max values. Both dataframe
have a Code column which is exactly similar.
Can I extract both min and max simultaneously or I have to combine two
dataframes?
I used the rbind and merge function but they did not give the desired
results.
> df3 = merge (df1, df2, by = "Code")
The result of this code adds a second dataframe as columns to the first
one. I want the first row of the second dataframe put below the first row
of the first dataframe and so on. I used a function to do this but it seems
it does not work correctly.

> fun2 = function(x,y){
                i = 1
                for(i in x) {
                      if (x[i,1] == y[i,1]){
                          rbind(x[i,],y[i,])
                          i = i+1
                }
                }
                }
> fun2(df1, df2)

Sincerely




























On Thu, Aug 25, 2022 at 9:08 PM <avi.e.gross using gmail.com> wrote:

> Yes, Timothy, the request was not seen by all of us as the same.
>
> Indeed if the request was to show a subset of the original data consisting
> of only the rows that were the minimum for each Code and also showed ties,
> then the solution is a tad more complex. I would then do something along
> the
> lines of what others showed such as generating another column showing the
> minimum for each row and then showing only rows that matched their value in
> two columns or whatever was needed.
>
> As noted, keeping the output in a specific order was not initially
> requested.
>
> Keeping the data in some order is a common enough request but in this
> situation, I suspect the order many might want would be the one showing the
> minimums in order, not the codes in the original order.
>
> -----Original Message-----
> From: Ebert,Timothy Aaron <tebert using ufl.edu>
> Sent: Thursday, August 25, 2022 11:59 AM
> To: avi.e.gross using gmail.com
> Cc: R-help using r-project.org
> Subject: RE: [R] Getting minimum value of a column according a factor
> column
> of a dataframe
>
> My assumption (maybe wrong) was that we needed to keep the other variables.
> I want to find the values of Y, M, D, N, and O for the minimum value of Q
> within each unique value of Code, keeping the data in the original order.
> All one need to do is filter Q in the original dataframe by your answer for
> minQ.
>
> Keeping the data in the original order seems unnecessary, but that is what
> was asked in a later post.
>
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Best Regards
Javad Bayat
M.Sc. Environment Engineering
Alternative Mail: bayat194 using yahoo.com

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