[R] Getting minimum value of a column according a factor column of a dataframe
@vi@e@gross m@iii@g oii gm@ii@com
@vi@e@gross m@iii@g oii gm@ii@com
Fri Aug 26 07:31:45 CEST 2022
What you mean, Bayat, is you only read and tried my first reply BEFORE you expanded your request! LOL!
I really appreciate reading what other’s write here and different approaches. Rui had a beautiful idea of doubling his rows as a way to retain the order of two requests. It could generalize to more.
From: javad bayat <j.bayat194 using gmail.com>
Sent: Friday, August 26, 2022 12:39 AM
To: Rui Barradas <ruipbarradas using sapo.pt>
Cc: avi.e.gross using gmail.com; R-help using r-project.org
Subject: Re: [R] Getting minimum value of a column according a factor column of a dataframe
Dear all;
Many thanks for your suggestions and answers. The problem was solved by the codes that Rui sent just now. Jim's codes also were correct but did not give the results in original order.
Dear avi.e.gross using gmail.co <mailto:avi.e.gross using gmail.co> , has provided codes but they just result in columns with max or min but they did not give the whole row's values related to the Q min.
Thank you so much again.
Sincerely
On Fri, Aug 26, 2022 at 8:44 AM Rui Barradas <ruipbarradas using sapo.pt <mailto:ruipbarradas using sapo.pt> > wrote:
Hello,
To return 2 rows for each Code, one for the min and another for the max,
try the following.
I'm borrowing Bert's by() idea, it makes everything simpler.
There is a hack to have the original Code order kept, since the final
result res should have two rows for each Code, see what is order()'ed below.
# the output has 2 consecutive rows with
# the same Code, so repeat the unique Codes
i <- order(rep(unique(df1$Code), each = 2))
res <- by(df1, df1$Code, \(x) x[c(which.min(x$Q), which.max(x$Q)), ])
res <- do.call(rbind, res)[order(i), ]
# remake the row names, they're ugly after rbind
row.names(res) <- NULL
res
Hope this helps,
Rui Barradas
Às 19:02 de 25/08/2022, javad bayat escreveu:
> ;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
>
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> On Thu, Aug 25, 2022 at 9:08 PM <avi.e.gross using gmail.com <mailto: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 <mailto:tebert using ufl.edu> >
>> Sent: Thursday, August 25, 2022 11:59 AM
>> To: avi.e.gross using gmail.com <mailto:avi.e.gross using gmail.com>
>> Cc: R-help using r-project.org <mailto: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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>> PLEASE do read the posting guide
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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 <mailto:bayat194 using yahoo.com>
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