CODEWITHSUNDEEP
rdata-analysisdata-manipulation
oivemaria
oivemaria

Reputation: 463

Changing values of multiple column elements for dataframe in R

I'm trying to update a bunch of columns by adding and subtracting SD to each value of the column. The SD is for the given column.

The below is the reproducible code that I came up with, but I feel this is not the most efficient way to do it. Could someone suggest me a better way to do this?

Essentially, there are 20 rows and 9 columns.I just need two separate dataframes one that has values for each column adjusted by adding SD of that column and the other by subtracting SD from each value of the column. 

##Example
##data frame containing 9 columns and 20 rows
Hi<-data.frame(replicate(9,sample(0:20,20,rep=TRUE)))  
##Standard Deviation calcualted for each row and stored in an object - i don't what this objcet is -vector, list, dataframe ?
Hi_SD<-apply(Hi,2,sd)
#data frame converted to matrix to allow addition of SD to each value
Hi_Matrix<-as.matrix(Hi,rownames.force=FALSE)
#a new object created that will store values(original+1SD) for each variable 
Hi_SDValues<-NULL
#variable re-created -contains sum of first column of matrix and first element of list. I have only done this for 2 columns for the purposes of this example. however, all columns would need to be recreated
Hi_SDValues$X1<-Hi_Matrix[,1]+Hi_SD[1]
Hi_SDValues$X2<-Hi_Matrix[,2]+Hi_SD[2]
#convert the object back to a dataframe
Hi_SDValues<-as.data.frame(Hi_SDValues)

##Repeat for one SD less
Hi_SDValues_Less<-NULL
Hi_SDValues_Less$X1<-Hi_Matrix[,1]-Hi_SD[1]
Hi_SDValues_Less$X2<-Hi_Matrix[,2]-Hi_SD[2]
Hi_SDValues_Less<-as.data.frame(Hi_SDValues_Less)

Upvotes: 4

Views: 457

Answers (2)

Arnaud A
Arnaud A

Reputation: 377

This is a job for sweep (type ?sweep in R for the documentation)

Hi <- data.frame(replicate(9,sample(0:20,20,rep=TRUE)))  
Hi_SD <- apply(Hi,2,sd)
Hi_SD_subtracted <- sweep(Hi, 2, Hi_SD)

Upvotes: 2

C_Z_
C_Z_

Reputation: 7796

You don't need to convert the dataframe to a matrix in order to add the SD

Hi<-data.frame(replicate(9,sample(0:20,20,rep=TRUE)))  
Hi_SD<-apply(Hi,2,sd) # Hi_SD is a named numeric vector

Hi_SDValues<-Hi # Creating a new dataframe that we will add the SDs to

# Loop through all columns (there are many ways to do this)
for (i in 1:9){
    Hi_SDValues[,i]<-Hi_SDValues[,i]+Hi_SD[i]
}
# Do pretty much the same thing for the next dataframe
Hi_SDValues_Less <- Hi
for (i in 1:9){
    Hi_SDValues[,i]<-Hi_SDValues[,i]-Hi_SD[i]
}

Upvotes: 1

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