Create a new variable based on existing variable

Question

My current dataset look like this

Order     V1     
1         7     
2         5    
3         8     
4         5  
5         8 
6         3    
7         4  
8         2     
1         8    
2         6 
3         3 
4         4 
5         5 
6         7 
7         3 
8         6

I want to create a new variable called "V2" based on the variables "Order" and "V1". For every 8 items in the "Order" variable, I want to assign a value of "0" in "V2" if the varialbe "Order" has observation equals to 1; otherwise, "V2" takes the value of previous item in "V1". This is the dataset that I want

Order    V1    V2
1        7     0
2        5     7
3        8     5
4        5     8
5        8     5
6        3     8
7        4     3
8        2     4
1        8     0
2        6     8
3        3     6
4        4     3
5        5     4
6        7     5
7        3     7
8        6     3

Since my actual dataset is very large, I'm trying to use for loop with if statement to generate "V2". But my code keeps failing. I appreciate if anyone can help me on this, and I'm open to other statements. Thank you!

r2evans · Accepted Answer · 2017-12-22 20:12:54Z

1

(Up front: I am assuming that the order of Order is perfectly controlled.)

You need simply ifelse and lag:

df <- read.table(text="Order     V1     
1         7     
2         5    
3         8     
4         5  
5         8 
6         3    
7         4  
8         2     
1         8    
2         6 
3         3 
4         4 
5         5 
6         7 
7         3 
8         6 ", header=T)

df$V2 <- ifelse(df$Order==1, 0, lag(df$V1))
df
#    Order V1 V2
# 1      1  7  0
# 2      2  5  7
# 3      3  8  5
# 4      4  5  8
# 5      5  8  5
# 6      6  3  8
# 7      7  4  3
# 8      8  2  4
# 9      1  8  0
# 10     2  6  8
# 11     3  3  6
# 12     4  4  3
# 13     5  5  4
# 14     6  7  5
# 15     7  3  7
# 16     8  6  3

edited Dec 22, 2017 at 20:12

answered Dec 22, 2017 at 20:08

r2evans

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1 Comment

pogibas Over a year ago

Or simple: ifelse(df$Order == 1, 0, c(NA, df$V1))

Onyambu · Accepted Answer · 2017-12-22 20:15:56Z

1

with(dat,{V2<-c(0,head(V1,-1));V2[Order==1]<-0;dat$V2<-V2;dat})
   Order V1 V2
1      1  7  0
2      2  5  7
3      3  8  5
4      4  5  8
5      5  8  5
6      6  3  8
7      7  4  3
8      8  2  4
9      1  8  0
10     2  6  8
11     3  3  6
12     4  4  3
13     5  5  4
14     6  7  5
15     7  3  7
16     8  6  3

answered Dec 22, 2017 at 20:15

Onyambu

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