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Merging two data frames with 3 common variables makes duplicated rows
3 messages · Rock Ouimet, Thomas Lumley, Rocko22
On Fri, 8 May 2009, Rock Ouimet wrote:
I am new to R (ex SAS user) , and I cannot merge two data frames without getting duplicated rows in the results. How to avoid this happening without using the unique() function? 1. First data frame is called "tmv" with 6 variables and 239 rows:
tmv[1:10,]
temps nom prenom sexe dist style 1 01:59:36 Cyr Steve H 45 free 2 02:09:55 Gosselin Erick H 45 free 3 02:12:18 Desfosses Sacha H 45 free 4 02:12:23 Lapointe Sebastien H 45 free 5 02:12:52 Labrie Michel H 45 free 6 02:12:54 Leblanc Michel H 45 free 7 02:13:02 Thibeault Sylvain H 45 free 8 02:13:49 Martel Stephane H 45 free 9 02:14:03 Lavoie Jean-Philippe H 45 free 10 02:14:05 Boivin Jean-Claude H 45 free Its structure is:
str(tmv)
'data.frame': 239 obs. of 6 variables: $ temps :Class 'times' atomic [1:239] 0.0831 0.0902 0.0919 0.0919 0.0923 ... .. ..- attr(*, "format")= chr "h:m:s" $ nom : Factor w/ 167 levels "Aubut","Audy",..: 45 84 55 105 98 110 158 117 109 22 ... $ prenom: Factor w/ 135 levels "Alain","Alexandre",..: 128 33 121 122 93 93 130 126 63 59 ... $ sexe : Factor w/ 2 levels "F","H": 2 2 2 2 2 2 2 2 2 2 ... $ dist : int 45 45 45 45 45 45 45 45 45 45 ... $ style : Factor w/ 2 levels "clas","free": 2 2 2 2 2 2 2 2 2 2 ... 2. The second data frame is called "meil2" with 4 variables and 16 rows;
meil2[1:10,]
dist sexe style meil 1 38 F clas 02:43:17 2 38 F free 02:24:46 3 38 H clas 02:37:36 4 38 H free 01:59:35 5 45 F clas 03:46:15 6 45 F free 02:20:15 7 45 H clas 02:30:07 8 45 H free 01:59:36 9 38 F clas 02:43:17 10 38 F free 02:24:46
Lines 9 and 1 appear to be the same in meil2, as do 2 and 10. If the 16 rows consist of two repeats of 8 rows that would explain why you are getting two copies of each individual in the output. unique(meil2) would have just the distinct rows.
-thomas
Thomas Lumley Assoc. Professor, Biostatistics
tlumley at u.washington.edu University of Washington, Seattle
Thomas, You are very clever! The "meil2" data frame has twice the common variable combinations:
meil2
dist sexe style meil 1 38 F clas 02:43:17 2 38 F free 02:24:46 3 38 H clas 02:37:36 4 38 H free 01:59:35 5 45 F clas 03:46:15 6 45 F free 02:20:15 7 45 H clas 02:30:07 8 45 H free 01:59:36 9 38 F clas 02:43:17 10 38 F free 02:24:46 11 38 H clas 02:37:36 12 38 H free 01:59:35 13 45 F clas 03:46:15 14 45 F free 02:20:15 15 45 H clas 02:30:07 16 45 H free 01:59:36 Keeping unique combinations merged correctly with the next data frame. This merge() function is more subtle than I first thought. That means when merging two data frames, if the resulting data frame has more rows than either former data frames, it means that there are duplicate combinations of the common variables in either or the two data frames. Thank you very much, I will try to be more careful about this. Rock
Thomas Lumley wrote:
On Fri, 8 May 2009, Rock Ouimet wrote:
I am new to R (ex SAS user) , and I cannot merge two data frames without getting duplicated rows in the results. How to avoid this happening without using the unique() function? 1. First data frame is called "tmv" with 6 variables and 239 rows:
tmv[1:10,]
temps nom prenom sexe dist style 1 01:59:36 Cyr Steve H 45 free 2 02:09:55 Gosselin Erick H 45 free 3 02:12:18 Desfosses Sacha H 45 free 4 02:12:23 Lapointe Sebastien H 45 free 5 02:12:52 Labrie Michel H 45 free 6 02:12:54 Leblanc Michel H 45 free 7 02:13:02 Thibeault Sylvain H 45 free 8 02:13:49 Martel Stephane H 45 free 9 02:14:03 Lavoie Jean-Philippe H 45 free 10 02:14:05 Boivin Jean-Claude H 45 free Its structure is:
str(tmv)
'data.frame': 239 obs. of 6 variables: $ temps :Class 'times' atomic [1:239] 0.0831 0.0902 0.0919 0.0919 0.0923 ... .. ..- attr(*, "format")= chr "h:m:s" $ nom : Factor w/ 167 levels "Aubut","Audy",..: 45 84 55 105 98 110 158 117 109 22 ... $ prenom: Factor w/ 135 levels "Alain","Alexandre",..: 128 33 121 122 93 93 130 126 63 59 ... $ sexe : Factor w/ 2 levels "F","H": 2 2 2 2 2 2 2 2 2 2 ... $ dist : int 45 45 45 45 45 45 45 45 45 45 ... $ style : Factor w/ 2 levels "clas","free": 2 2 2 2 2 2 2 2 2 2 ... 2. The second data frame is called "meil2" with 4 variables and 16 rows;
meil2[1:10,]
dist sexe style meil 1 38 F clas 02:43:17 2 38 F free 02:24:46 3 38 H clas 02:37:36 4 38 H free 01:59:35 5 45 F clas 03:46:15 6 45 F free 02:20:15 7 45 H clas 02:30:07 8 45 H free 01:59:36 9 38 F clas 02:43:17 10 38 F free 02:24:46
Lines 9 and 1 appear to be the same in meil2, as do 2 and 10. If the 16
rows consist of two repeats of 8 rows that would explain why you are
getting two copies of each individual in the output. unique(meil2) would
have just the distinct rows.
-thomas
Thomas Lumley Assoc. Professor, Biostatistics
tlumley at u.washington.edu University of Washington, Seattle
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