If you are looking for negative indexing by name (in addition to [tcash21&#39;s numeric indexing][1]), here&#39;s a few ways I know, some riskier than others:

    mtcars[, -which(names(mtcars) == &quot;carb&quot;)]  #only works on a single column
    mtcars[, names(mtcars) != &quot;carb&quot;]          #only works on a single column
    mtcars[, !names(mtcars) %in% c(&quot;carb&quot;, &quot;mpg&quot;)] 
    mtcars[, -match(c(&quot;carb&quot;, &quot;mpg&quot;), names(mtcars))] 
    mtcars2 &lt;- mtcars; mtcars2$hp &lt;- NULL         #lost column (risky)
    
    
    library(gdata) 
    remove.vars(mtcars2, names=c(&quot;mpg&quot;, &quot;carb&quot;), info=TRUE) 

Generally I use:

    mtcars[, !names(mtcars) %in% c(&quot;carb&quot;, &quot;mpg&quot;)] 
because I feel it&#39;s safe and efficient.


  [1]: https://stackoverflow.com/a/12868602/6409572

You can index and use a negative sign to drop the 3rd column:

    data[,-3]

Or you can list only the first 2 columns:

    data[,c(&quot;c1&quot;, &quot;c2&quot;)]
    data[,1:2]

Don&#39;t forget the comma and referencing data frames works like this: `data[row,column]`



I&#39;m trying to get the first key and value key from a hash table in ruby. I don&#39;t know the key values of the hash because it is passed to the method. I cant find anywhere online how to find the first key/value as a separate hash table. 
I think `hash[0]` will just try to find an element with a name 0 it just returns `nil` when I run the code. 

I know I can find the key name and the value and then create a new hash from them but i wonder if there is an easier way to do this so I get a hash right away. 

here is my code: 

    def rps_game_winner(game)
    
    rock_in_hash = game.invert[&#39;R&#39;]
    paper_in_hash = game.invert[&#39;P&#39;]
    scissors_in_hash = game.invert[&#39;S&#39;]
    
    if(rock_in_hash)
          if(paper_in_hash)
        	return paper_in_hash;
          elsif(scissors_in_hash)
        	return rock_in_hash
          end
        elsif(paper_in_hash)
          if(rock_in_hash)
        	return paper_in_hash
          elsif(scissors_in_hash)
        	return scissors_in_hash
          end
        end
        	key = game.keys[-1]
         	value = game.values[-1]
    	    	winner = {key =&gt; value}
        return winner 
        end

    game_one = { &quot;Bob&quot; =&gt; &#39;P&#39;, &quot;Jim&quot; =&gt; &#39;P&#39; }
    
    puts rps_game_winner(game_one)

This gets me the correct result the problem is I don&#39;t understand why it&#39;s -1 instead of zero...
And i was hoping there was a better way to get the first key/value pair of a hash table instead of creating new hash table with the key and value you retrieved from the previous table. 

How to get the first key and value pair from a hash table in Ruby

I&#39;m using JPEGCAM to allow users to take a profile pic with their web cam. This uploads a temporary file as so:


    def ajax_photo_upload    
      File.open(upload_path, &#39;w:ASCII-8BIT&#39;) do |f|
        f.write request.raw_post
      end
      # @user.photo = File.open(upload_path)
      @user.assign_attributes(
        :photo =&gt; File.open(upload_path),
        :orig_filename =&gt; &quot;#{current_user.full_name}.jpg&quot;
      )
      if @user.save
      respond_to do |format|
      .....
    private
    
      def upload_path # is used in upload and create
        file_name = session[:session_id].to_s + &#39;.jpg&#39;
        File.join(::Rails.root.to_s, &#39;public&#39;, &#39;temp&#39;, file_name)
      end

What&#39;s the best way to go about deleting this temporary file safely? Thanks

Rails how to delete a file without failing on error

&gt; **Possible Duplicate:**  
&gt; [Drop Columns R Data frame](https://stackoverflow.com/questions/4605206/drop-columns-r-data-frame)  

&lt;!-- End of automatically inserted text --&gt;

Let&#39;s say I have a dataframe with column c1, c2, c3.

I want to list just c1 and c2. How do I do that?

I&#39;ve tried:

    head(data[column!=&quot;c3&quot;])
    head(data)[,2]
    head(data[!&quot;c3&quot;])

List all column except for one in R

> Possible Duplicate: 
> <a href="https://stackoverflow.com/questions/4605206/drop-columns-r-data-frame" target="_blank" rel="noopener noreferrer">Drop Columns R Data frame</a>

Let's say I have a dataframe with column c1, c2, c3.
I want to list just c1 and c2. How do I do that?
I've tried:
<pre><code class="hljs language-scss">head(data[column!="c3"])
head(data)[,2]
head(data[!"c3"])
</code></pre>

Working with a data frame similar to this:  

    set.seed(100)  
    df &lt;- data.frame(cat = c(rep(&quot;aaa&quot;, 5), rep(&quot;bbb&quot;, 5), rep(&quot;ccc&quot;, 5)), val = runif(15))             
    df &lt;- df[order(df$cat, df$val), ]  
    df  

       cat        val  
    1  aaa 0.05638315  
    2  aaa 0.25767250  
    3  aaa 0.30776611  
    4  aaa 0.46854928  
    5  aaa 0.55232243  
    6  bbb 0.17026205  
    7  bbb 0.37032054  
    8  bbb 0.48377074  
    9  bbb 0.54655860  
    10 bbb 0.81240262  
    11 ccc 0.28035384  
    12 ccc 0.39848790  
    13 ccc 0.62499648  
    14 ccc 0.76255108  
    15 ccc 0.88216552 

   
I am trying to add a column with numbering within each group. Doing it this way obviously isn&#39;t using the powers of R:  
  

     df$num &lt;- 1  
     for (i in 2:(length(df[,1]))) {  
       if (df[i,&quot;cat&quot;]==df[(i-1),&quot;cat&quot;]) {  
         df[i,&quot;num&quot;]&lt;-df[i-1,&quot;num&quot;]+1  
         }  
     }  
     df  

       cat        val num  
    1  aaa 0.05638315   1  
    2  aaa 0.25767250   2  
    3  aaa 0.30776611   3  
    4  aaa 0.46854928   4  
    5  aaa 0.55232243   5  
    6  bbb 0.17026205   1  
    7  bbb 0.37032054   2  
    8  bbb 0.48377074   3  
    9  bbb 0.54655860   4  
    10 bbb 0.81240262   5  
    11 ccc 0.28035384   1  
    12 ccc 0.39848790   2  
    13 ccc 0.62499648   3  
    14 ccc 0.76255108   4  
    15 ccc 0.88216552   5  

  
What would be a good way to do this?






Numbering rows within groups in a data frame

I understand that `XLConnect` can be used to read an Excel worksheet into R. For example, this would read the first worksheet in a workbook called `test.xls` into R.

    library(XLConnect)
    readWorksheetFromFile(&#39;test.xls&#39;, sheet = 1)

I have an Excel Workbook with multiple worksheets. 

How can all worksheets in a workbook be imported into a list in R where each element of the list is a data.frame for a given sheet, and where the name of each element corresponds to the name of the worksheet in Excel?


Read all worksheets in an Excel workbook into an R list with data.frames

I am using the `twang` package to create propensity scores, which are used as weights in a binomial glm using `survey::svyglm`. The code looks something like this:

    pscore &lt;- ps(ppci ~ var1+var2+.........., data=dt....)

    dt$w &lt;- get.weights(pscore, stop.method=&quot;es.mean&quot;)

    design.ps &lt;- svydesign(ids=~1, weights=~w, data=dt,)

    glm1 &lt;- svyglm(m30 ~ ppci, design=design.ps,family=binomial)

This produces the following warning:

    Warning message:
       In eval(expr, envir, enclos) : non-integer #successes in a binomial glm!

Does anyone know what I could be doing wrong ?

I wasn&#39;t sure if this message would be better on stats.SE, but on balance I thought I would try here first.

Warning: non-integer #successes in a binomial glm! (survey packages)

Everyone else&#39;s functions seem to take formula objects and then do dark magic to them somewhere deep inside and I&#39;m jealous. 

I&#39;m writing a function that fits multiple models. Parts of the formulas for these models remain the same and part change from one model to the next. The clumsy way would be to have the user input the formula parts as character strings, do some character manipulation on them, and then use `as.formula`.

But before I go that route, I just want to make sure that I&#39;m not overlooking some cleaner way of doing it that would allow the function to accept formulas in the standard R format (e.g. extracted from other formula-using objects).

I want something like...

    &gt; LHS &lt;- y~1; RHS &lt;- ~a+b; c(LHS,RHS);
    y ~ a + b
    &gt; RHS2 &lt;- ~c;
    &gt; c(LHS, RHS, RHS2);
    y ~ a + b + c

or...

    &gt; LHS + RHS;
    y ~ a + b
    &gt; LHS + RHS + RHS2;
    y ~ a + b + c

...but unfortunately neither syntax works. Does anybody know if there is something that does? Thanks.

Is there a better alternative than string manipulation to programmatically build formulas?

I would like to put perpendicular lines at the ends of the whiskers like the `boxplot` function automatically gives.



Put whisker ends on boxplot

In R when you need to retrieve a column index based on the name of the column you could do

    idx &lt;- which(names(my_data)==my_colum_name)

Is there a way to do the same with pandas dataframes?

Get column index from column name in python pandas

How to remove rows with duplicate index values?

In the weather DataFrame below, sometimes a scientist goes back and corrects observations -- not by editing the erroneous rows, but by appending a duplicate row to the end of a file.

I&#39;m reading some automated weather data from the web (observations occur every 5 minutes, and compiled into monthly files for each weather station.) After parsing a file, the DataFrame looks like:

                          Sta  Precip1hr  Precip5min  Temp  DewPnt  WindSpd  WindDir  AtmPress
    Date                                                                                      
    2001-01-01 00:00:00  KPDX          0           0     4       3        0        0     30.31
    2001-01-01 00:05:00  KPDX          0           0     4       3        0        0     30.30
    2001-01-01 00:10:00  KPDX          0           0     4       3        4       80     30.30
    2001-01-01 00:15:00  KPDX          0           0     3       2        5       90     30.30
    2001-01-01 00:20:00  KPDX          0           0     3       2       10      110     30.28

Example of a duplicate case:

    import pandas 
    import datetime

    startdate = datetime.datetime(2001, 1, 1, 0, 0)
    enddate = datetime.datetime(2001, 1, 1, 5, 0)
    index = pandas.DatetimeIndex(start=startdate, end=enddate, freq=&#39;H&#39;)
    data1 = {&#39;A&#39; : range(6), &#39;B&#39; : range(6)}
    data2 = {&#39;A&#39; : [20, -30, 40], &#39;B&#39; : [-50, 60, -70]}
    df1 = pandas.DataFrame(data=data1, index=index)
    df2 = pandas.DataFrame(data=data2, index=index[:3])
    df3 = df2.append(df1)

    df3
                           A   B
    2001-01-01 00:00:00   20 -50
    2001-01-01 01:00:00  -30  60
    2001-01-01 02:00:00   40 -70
    2001-01-01 03:00:00    3   3
    2001-01-01 04:00:00    4   4
    2001-01-01 05:00:00    5   5
    2001-01-01 00:00:00    0   0
    2001-01-01 01:00:00    1   1
    2001-01-01 02:00:00    2   2




And so I need `df3` to eventually become:

                           A   B
    2001-01-01 00:00:00    0   0
    2001-01-01 01:00:00    1   1
    2001-01-01 02:00:00    2   2
    2001-01-01 03:00:00    3   3
    2001-01-01 04:00:00    4   4
    2001-01-01 05:00:00    5   5

I thought that adding a column of row numbers (`df3[&#39;rownum&#39;] = range(df3.shape[0])`) would help me select the bottom-most row for any value of the `DatetimeIndex`, but I am stuck on figuring out the `group_by` or `pivot` (or ???) statements to make that work.


Remove pandas rows with duplicate indices

I have the following `DataFrame` (`df`):

    import numpy as np
    import pandas as pd
    
    df = pd.DataFrame(np.random.rand(10, 5))

I add more column(s) by assignment:

    df[&#39;mean&#39;] = df.mean(1)

How can I move the column `mean` to the front, i.e. set it as first column leaving the order of the other columns untouched?

How to change the order of DataFrame columns?

I am interested in knowing how to convert a pandas dataframe into a NumPy array.

dataframe:

    import numpy as np
    import pandas as pd

    index = [1, 2, 3, 4, 5, 6, 7]
    a = [np.nan, np.nan, np.nan, 0.1, 0.1, 0.1, 0.1]
    b = [0.2, np.nan, 0.2, 0.2, 0.2, np.nan, np.nan]
    c = [np.nan, 0.5, 0.5, np.nan, 0.5, 0.5, np.nan]
    df = pd.DataFrame({&#39;A&#39;: a, &#39;B&#39;: b, &#39;C&#39;: c}, index=index)
    df = df.rename_axis(&#39;ID&#39;)
  
gives

    label   A    B    C
    ID                                 
    1	NaN  0.2  NaN
    2	NaN  NaN  0.5
    3	NaN  0.2  0.5
    4	0.1  0.2  NaN
    5	0.1  0.2  0.5
    6	0.1  NaN  0.5
    7	0.1  NaN  NaN

I would like to convert this to a NumPy array, as so:

    array([[ nan,  0.2,  nan],
           [ nan,  nan,  0.5],
           [ nan,  0.2,  0.5],
           [ 0.1,  0.2,  nan],
           [ 0.1,  0.2,  0.5],
           [ 0.1,  nan,  0.5],
           [ 0.1,  nan,  nan]])

How can I do this? 

----

As a bonus, is it possible to preserve the dtypes, like this?
 
    array([[ 1, nan,  0.2,  nan],
           [ 2, nan,  nan,  0.5],
           [ 3, nan,  0.2,  0.5],
           [ 4, 0.1,  0.2,  nan],
           [ 5, 0.1,  0.2,  0.5],
           [ 6, 0.1,  nan,  0.5],
           [ 7, 0.1,  nan,  nan]],
         dtype=[(&#39;ID&#39;, &#39;&lt;i4&#39;), (&#39;A&#39;, &#39;&lt;f8&#39;), (&#39;B&#39;, &#39;&lt;f8&#39;), (&#39;B&#39;, &#39;&lt;f8&#39;)])

or similar?


Content Type	Original Author	Original Content on Stackoverflow
Question	mythicalprogrammer	View Question on Stackoverflow
Solution 1 - R	Tyler Rinker	View Answer on Stackoverflow
Solution 2 - R	tcash21	View Answer on Stackoverflow

List all column except for one in R

R Problem Overview

R Solutions

Solution 1 - R

Solution 2 - R

Rails how to delete a file without failing on error

How to get the first key and value pair from a hash table in Ruby

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