CODEWITHSUNDEEP
r
Paula
Paula

Reputation: 3

Create a new column with a sum based on the value of three other columns

I have a data frame and I want to create another column based on the information of three different columns. I am using R.

I want to start counting on 0 and to add 2 in each new cell, based on a column Time and on Item and Participants information. I want to have 0 for the beginning of the Time counting (which is in ms) for each item of each participant. 

df <- data.frame(Item=c(1,1,1,1,1,1,2,2,2,2,2,2),  
             Part=c(1,1,1,2,2,2,1,1,1,2,2,2), 
            Time=c(1234,1235,1236,345,346,347,1546,1547,1548,234,235,236))

   Item Part Time
1     1    1 1234
2     1    1 1235
3     1    1 1236
4     1    2  345
5     1    2  346
6     1    2  347
7     2    1 1546
8     2    1 1547
9     2    1 1548
10    2    2  234
11    2    2  235
12    2    2  236

With the new column the table would be something like:

   Item Part Time NewColumn
1     1    1 1234         0
2     1    1 1235         2
3     1    1 1236         4
4     1    2  345         0
5     1    2  346         2
6     1    2  347         4
7     2    1 1546         0
8     2    1 1547         2
9     2    1 1548         4
10    2    2  234         0
11    2    2  235         2
12    2    2  236         4

Many thanks in advance.

Upvotes: 0

Views: 527

Answers (4)

Amrita Sawant
Amrita Sawant

Reputation: 10913

+1 for library(plyr)

    library(plyr)
    ddply(df, c("Item","Part"), mutate,NewColumn = seq(0,4,2))



    Item Part   Time NewColumn
     1    1     1234    0
     1    1     1235    2
     1    1     1236    4
     1    2     345     0
     1    2     346     2
     1    2     347     4
     2    1     1546    0
     2    1     1547    2
     2    1     1548    4
     2    2     234     0
     2    2     235     2
     2    2     236     4

Upvotes: 1

rmuc8
rmuc8

Reputation: 2989

In case the structure stays as it is

library(dplyr)
result <- df %>% group_by(Part, Item) %>% mutate(NewColumn = seq (0,4,2))

I group by Item and Part and create a new column that counts 0, 2, 4

   Item Part Time NewColumn
1     1    1 1234         0
2     1    1 1235         2
3     1    1 1236         4
4     1    2  345         0
5     1    2  346         2
6     1    2  347         4
7     2    1 1546         0
8     2    1 1547         2
9     2    1 1548         4
10    2    2  234         0
11    2    2  235         2
12    2    2  236         4

In order to be more flexible (if you have more than 3 rows per group), you can use

result <- df %>% group_by(Part, Item) %>% mutate(NewColumn = 2* (row_number()-1))

which will will generate numbers in the sequence 0, 2, 4, 6, 8,...

Upvotes: 4

jaybee
jaybee

Reputation: 955

Er... df = cbind(df,NewColumn=c(0,2,4))?

Upvotes: 1

pogibas
pogibas

Reputation: 28309

library(data.table)
df <- data.table(df)
df[, NewCol := seq(0,nrow(df),2), by=list(Item,Part)]

Upvotes: 2

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