[R] nested if/else very slow, more efficient ways?

[Kim Milferstedt]

Hi Alex,

find below a sample of the input and the desired output of my data. 
5a ... 5e are indeed the only possible values for the column in 
question. I would like to replace 5a --> 1, 55b --> 2, ... 5e --> 5.

Kim

## input ###

Image_ID                        Class   Max     1       2       3 
   4       5       exp
060901_1545_17_1_10.tif 5c      0.82329 0.32734 0.12593 0.50405 
0.03987 0.00282 1.7
060902_1570_01_1_01.tif 5a      0.65336 0.59857 0.10341 0.25193 
0.04384 0.00225 1.7
060902_1570_01_1_02.tif 5c      0.57736 0.22884 0.08554 0.65148 
0.03091 0.00323 1.7
060902_1570_01_1_03.tif 5a      0.28857 0.83517 0.02118 0.12374 
0.018   0.00191 1.7
060902_1570_01_1_04.tif 5b      0.58386 0.12772 0.60949 0.19336 
0.06501 0.00442 1.7
060902_1570_01_1_05.tif 5c      0.83419 0.3594  0.08062 
0.5252  0.03211 0.00267 1.7
060902_1570_01_1_06.tif 5c      0.61535 0.27652 0.04082 0.66117 
0.01933 0.00217 1.7
060902_1570_01_1_07.tif 5c      0.22709 0.0969  0.02196 0.86981 
0.00985 0.00149 1.7
060902_1570_01_1_08.tif 5c      0.24596 0.10647 0.02151 0.86051 
0.01    0.00151 1.7
060902_1570_01_1_09.tif 5a      0.92945 0.48802 0.04582 0.41747 
0.03852 0.01017 1.7
060902_1570_01_1_10.tif 5a      0.49169 0.71852 0.03417 
0.2102  0.03203 0.00508 1.7
060902_1570_06_1_01.tif 5b      0.1927  0.05284 0.86286 0.02789 
0.05556 0.00085 1.7
060902_1570_06_1_02.tif 5a      0.12993 0.91879 0.01481 0.04872 
0.01643 0.00125 1.7

## output ###

Image_ID                        Class   Max     1       2       3 
   4       5       exp
060901_1545_17_1_10.tif 3       0.82329 0.32734 0.12593 0.50405 
0.03987 0.00282 1.7
060902_1570_01_1_01.tif 1       0.65336 0.59857 0.10341 0.25193 
0.04384 0.00225 1.7
060902_1570_01_1_02.tif 3       0.57736 0.22884 0.08554 0.65148 
0.03091 0.00323 1.7
060902_1570_01_1_03.tif 1       0.28857 0.83517 0.02118 0.12374 
0.018   0.00191 1.7
060902_1570_01_1_04.tif 2       0.58386 0.12772 0.60949 0.19336 
0.06501 0.00442 1.7
060902_1570_01_1_05.tif 3       0.83419 0.3594  0.08062 
0.5252  0.03211 0.00267 1.7
060902_1570_01_1_06.tif 3       0.61535 0.27652 0.04082 0.66117 
0.01933 0.00217 1.7
060902_1570_01_1_07.tif 3       0.22709 0.0969  0.02196 0.86981 
0.00985 0.00149 1.7
060902_1570_01_1_08.tif 3       0.24596 0.10647 0.02151 0.86051 
0.01    0.00151 1.7
060902_1570_01_1_09.tif 1       0.92945 0.48802 0.04582 0.41747 
0.03852 0.01017 1.7
060902_1570_01_1_10.tif 1       0.49169 0.71852 0.03417 
0.2102  0.03203 0.00508 1.7
060902_1570_06_1_01.tif 2       0.1927  0.05284 0.86286 0.02789 
0.05556 0.00085 1.7
060902_1570_06_1_02.tif 1       0.12993 0.91879 0.01481 0.04872 
0.01643 0.00125 1.7


At 17:23 06/10/23, you wrote:
>There are a number of ways this might be approached.
>
>Can you please give a sample of your data, and your desired output?
>
>Are "5a" ... "5e" the only values that appear in that column, or are
>there other values, "4e" for instance, that should stay the same
>during your conversion?
>
>Do you wish to use the numbers 1 to 5 in the processed column in
>arithmetic processing, or are they just an enumeration of possible
>values?
>
>While you think about it, I direct your attention to the functions:
>
>sub
>factor
>
>-Alex
>
>On 23 Oct 2006, at 23:03, Kim Milferstedt wrote:
>
>>Hello,
>>
>>in the data.frame "resultsfuzzy" I would like to replace the
>>characters in the second column ("5a", "5b", ... "5e") with numbers
>>from 1 to 5. The data.frame has 39150 entries. I seems to work on
>>samples that are << nrow(resultsfuzzy) but it takes suspicously long.
>>
>>Do you have any suggestions how to make the character replacing
>>more efficient?
>>
>>Code:
>>
>>for (i in 1:nrow(resultsfuzzy))
>>{
>>if (resultsfuzzy[i,2] == "5a"){resultsfuzzy[i,2] <- 1} else
>>      if (resultsfuzzy[i,2] == "5b"){resultsfuzzy[i,2] <- 2} else
>>          if (resultsfuzzy[i,2] == "5c"){resultsfuzzy[i,2] <- 3} else
>>              if (resultsfuzzy[i,2] == "5d"){resultsfuzzy[i,2] <- 4}
>>else
>>                  resultsfuzzy[i,2] <- 5
>>}
>>
>>Thanks,
>>
>>Kim
>>
>>version
>>
>>platform i386-pc-mingw32
>>arch     i386
>>os       mingw32
>>system   i386, mingw32
>>status
>>major    2
>>minor    2.1
>>year     2005
>>month    12
>>day      20
>>svn rev  36812
>>language R
>>
>>__________________________________________
>>
>>Kim Milferstedt
>>University of Illinois at Urbana-Champaign
>>Department of Civil and Environmental Engineering
>>4125 Newmark Civil Engineering Laboratory
>>205 North Mathews Avenue MC-250
>>Urbana, IL 61801
>>USA
>>phone: (001) 217 333-9663
>>fax: (001) 217 333-6968
>>email: milferst at uiuc.edu
>>http://cee.uiuc.edu/research/morgenroth
>>
>>______________________________________________
>>R-help at stat.math.ethz.ch mailing list
>>https://stat.ethz.ch/mailman/listinfo/r-help
>>PLEASE do read the posting guide http://www.R-project.org/posting- guide.html
>>and provide commented, minimal, self-contained, reproducible code.