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MCAR and MNAR

MCAR is an acronym for Missing Completely at Random MNAR means Missing not at Random When you have data missing you may try to check if this missing data is random or not. Usually this is done by checking the… Continue Reading →

Difference between Pearson and Spearman correlation

Spearman rank correlation method Better use when: variables are not normally distributed or the relationship between the variables is not linear  

Remove a column from a R dataframe

To remove a column from a R dataframe you have to check what is the column number and then give command like data<-data[,-1] The number will be the column to be deleted.

Correlation in R

The correlation coefficient of two variables in a data sample is their covariance divided by the product of their individual standard deviations. It is a normalized measurement of how the two are linearly related with values beetween -1 and 1. To calculate… Continue Reading →

Format output of summary

You can use function lapply() to apply function summary() to each column and then cbind() to show data as column. lapply(dataFrame,function(x) cbind(summary(x))) From http://stackoverflow.com/questions/14791075/r-format-data-frame-summary

Better way to present correlations

http://www.r-bloggers.com/more-on-exploring-correlations-in-r/ cor() – table of correlations cor.prob() – Replaces the upper triangul with the significance flattenSquareMatrix(cor.prob(mydata)) – makes a table out of it   flattenSquareMatrix <- function(m) { if( (class(m) != “matrix“) | (nrow(m) != ncol(m))) stop(“Must be a square… Continue Reading →

Dataframe to matrix

To pass a dataframe in R to matrix as.matrix(mtcars) Some commands work over matrix and not over dataframes

Copy data from Excel to R

After selecting and copying the data to clipboard in Excel just do read.excel <- function(header=TRUE,…) { read.table(“clipboard”,sep=”\t”,header=header,…) }   dat=read.excel() More details in http://alandgraf.blogspot.com.es/2013/02/copying-data-from-excel-to-r-and-back_24.html

Correlation is not causation

correlation is not causation

Simple test for the mean

For doing a test for the mean of a normal distributed variable in R do: t.test(variable, mu=55) mu= 55 is the value of the meaning that you want to test   The output is something like: One Sample t-test data: variable… Continue Reading →

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