[R] Add a column to a dataframe based on multiple other column values

[arun]

HI,
May be this helps:
dat1<- read.table(text="
x1    y1    x2    y2    x3    y3    output
2    100    190    99    1430    79    89
2    100    192    63    1431    75    69
2    100    192    63    1444    51    57
3    0    195    99    1499    50    74.5
3    0    198    98    1500    80    89
30    0    198    100    1451    97    65.66666667
32    100    868    100    1451    97    99
33    82    870    100    1490    97    93
33    0    871    82    1494    85    55.66666667
",sep="",header=TRUE)

dat1$output2<-apply(dat1[,-7],1,function(x) {indx<-((seq(x)-1)%%2+1);indx1<-indx==1; indx2<-indx==2;mean(x[indx2][x[indx1]>10])})
 dat1
#  x1  y1  x2  y2   x3 y3   output  output2
#1  2 100 190  99 1430 79 89.00000 89.00000
#2  2 100 192  63 1431 75 69.00000 69.00000
#3  2 100 192  63 1444 51 57.00000 57.00000
#4  3   0 195  99 1499 50 74.50000 74.50000
#5  3   0 198  98 1500 80 89.00000 89.00000
#6 30   0 198 100 1451 97 65.66667 65.66667
#7 32 100 868 100 1451 97 99.00000 99.00000
#8 33  82 870 100 1490 97 93.00000 93.00000
#9 33   0 871  82 1494 85 55.66667 55.66667
A.K.



----- Original Message -----
From: Tom Oates <toates19 at gmail.com>
To: r-help at r-project.org
Cc: 
Sent: Tuesday, June 11, 2013 12:07 PM
Subject: [R] Add a column to a dataframe based on multiple other column
	values

Hi
I have a dataframe as below:

x1    y1    x2    y2    x3    y3    output
2    100    190    99    1430    79    89
2    100    192    63    1431    75    69
2    100    192    63    1444    51    57
3    0    195    99    1499    50    74.5
3    0    198    98    1500    80    89
30    0    198    100    1451    97    65.66666667
32    100    868    100    1451    97    99
33    82    870    100    1490    97    93
33    0    871    82    1494    85    55.66666667


In reality the dataframe has pairs of columns x & y up to a large number.
As you can see from the column labelled output in the dataframe; I want to
calculate the mean of each row of the yn columns, but only to include each
yn value in the calculation of the mean if the corresponding xn column
value is greater than 10.
So for row 1; you will see that only y2 & y3 are included in calculating
the output column, but for row 6 y1-y3 are all included.
Because the number of paired x & y columns is large I am not sure the best
way to achieve this.
Thanks in advance
Tom

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