update a column in dataframe based on another dataframe

Question

I have dataframe

df1 ->

ID Name
1  Test1
2  Test2
3  Test3

I have another dataframe df2

df2 ->

ID Name
1  Char
2  Float
3  Decimal
4  String

Now I want to update df1 name values based on names from df2 using ID

Now my df1 output should be

ID Name
1  Char
2  Float
3  Decimal

Please let me know how to acheive this.

I would try to be clearer about whether you want to do a lookup by ID, or just match identically numbered rows. — Jack Wasey, Nov 17 '15 at 02:13

score 4 · Answer 1 · edited Nov 17 '15 at 02:17

4

We can use match

df1$Name <- df2$Name[match(df1$ID, df2$ID)]

Or as @thelatemail mentioned, this can be solved with merge

merge(df1["ID"], df2, all.x=TRUE)

edited Nov 17 '15 at 02:17

thelatemail

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answered Nov 17 '15 at 02:11

akrun

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2

Also `merge` - `merge(df1["ID"], df2, all.x=TRUE)` – thelatemail Nov 17 '15 at 02:13

score 2 · Answer 2 · answered Nov 17 '15 at 02:49

2

Another option:

library(qdapTools)
df1$Name <- df1$ID %l% df2

answered Nov 17 '15 at 02:49

Steven Beaupré

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Adam Birenbaum · Answer 3 · 2015-11-17T01:59:53.830

0

Not sure if you were looking for something besides simply this:

df1$Name <- df2$Name[1:3]

edited Nov 17 '15 at 01:59

answered Nov 17 '15 at 01:49

Adam Birenbaum

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score 0 · Answer 4 · answered Mar 27 '17 at 07:39

Use the ID to get the right names.

df1$Name <- df2$Name[df1$ID]

Note that this solution is applicable if the number of observations in df1 is less than or equals to the number of observations in df2, otherwise, you will end up with NA. Also, the ID is the row number.

update a column in dataframe based on another dataframe

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