[R] Comparing Variables and Writing a New Column

[Jerry Floren]

HI,

I am using Windows XP and R version 2.9.2. I have a data frame written by R
similar to the following:

Lab_ID    Analysis_Soil        Results        -4MAD      -2.5MAD     
+2.5MAD        +4MAD
55003    Calcium-2008-116      900             961        1121.5        
1656.5          1817
55003    Calcium-2008-117     3321           2175        2380.5        
3065.5          3271
55003    Calcium-2008-118     3342           3155        4019           
6899            7763
55003    Calcium-2008-119     1664          1005.6     1147.92       1622.32        
1764.64
55003    Calcium-2008-120     2570          1880        2072            2712           
2904

Previously, I took this table and finished my analysis in Excel using
Excel's "=if" function. However, I am sure it can be done in R. What I want
to do is set up a new data.frame with a new column for Accuracy Flags
(a_flag) as shown below.

Lab_ID    Analysis_Soil        Results        -4MAD      -2.5MAD     
+2.5MAD        +4MAD        a_flag
55003    Calcium-2008-116      900             961        1121.5        
1656.5          1817         **L
55003    Calcium-2008-117     3321           2175        2380.5        
3065.5          3271         **H
55003    Calcium-2008-118     3342           3155        4019           
6899            7763           *L
55003    Calcium-2008-119     1664          1005.6     1147.92       1622.32         
1764.64      *H
55003    Calcium-2008-120     2570          1880        2072            2712            
2904

For each row I need to compare the "Results" submitted by the labs to the
four "MAD" columns. If the Results are less than -4.0 MAD units from the
median, labs are flagged "**L" (very low). For results greater than +4.0 MAD
units, labs are flagged "**H" (very high). Likewise for -2.5 MAD and +2.5
MAD (*L and *H respectively). As shown in the last row, labs are not flagged
for results within -2.5 MAD to +2.5 MAD units.

Can anyone get me started on how to look at each row and compare the
"Results" variable with each of the four "__MAD" variables and then writing
the appriate flag for Results exceeding -2.5 MAD to +2.5 MAD units from the
median?

Thanks,

Jerry Floren
Minnesota Department of Agriculture







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