pamr.train               package:pamr               R Documentation

_A _f_u_n_c_t_i_o_n _t_o _t_r_a_i_n _a _n_e_a_r_e_s_t _s_h_r_u_n_k_e_n _c_e_n_t_r_o_i_d
_c_l_a_s_s_i_f_i_e_r

_D_e_s_c_r_i_p_t_i_o_n:

     A function that computes a nearest shrunken centroid for gene
     expression (microarray) data

_U_s_a_g_e:

     pamr.traindata, gene.subset = 1:nrow(data$x), sample.subset =
                      1:ncol(data$x), threshold = NULL, n.threshold = 30,
                      scale.sd = TRUE, threshold.scale = NULL, se.scale =
                      NULL, offset.percent = 50, prior = NULL, remove.zeros
                      = TRUE, sign.contrast = "both")

_A_r_g_u_m_e_n_t_s:

    data: The input data. A list with components: x- an expression
          genes in the rows, samples in the columns), and y-  a vector
          of the class labels for each sample

gene.subset: Subset of genes to be used.  Can be either a logical
          vector of length total number of genes, or a list of integers
          of the row numbers of the genes to be used

sample.subset: 

threshold: A vector of threshold values for the centroid shrinkage.
          Default is a set of 30 values chosen by the software

n.threshold: Number of threshold values desired (default 30)

scale.sd: Scale each threshold by the wthin class standard deviations?
          Default: true

threshold.scale: Additional scaling factors to be applied to the
          thresholds. Vector of length equal to the number of classes.
          Default- a vectors of ones.

se.scale: Vector of scaling factors for the within class standard
          errors. Default is sqrt(1/n.class-1/n), where n is the
          overall sample size and n.class is the sample sizes in each
          class. This default adjusts for different class sizes.

offset.percent: Fudge factor added to  the denominator of each
          t-statistic, expressed as a percentile of the gene standard
          deviation values. This is a small positive quantity to
          penalize genes with expression values near zero, which can
          result in very large ratios. This factor is expecially
          impotant for Affy data. Default is the median of the standard
          deviations of each gene.

   prior: Vector of length the number of classes, representing prior
          probabilities for each of the classes. The prior is used in
          Bayes rule for making class prediction. Default is n.class/n,
          where  n is the overall sample size and n.class is the sample
          sizes in   each class.

remove.zeros: Whether to remove multiple solutions having zero genes

sign.contrast: Directions of allowed deviations of class-wise average
          gene  expression from the  overall average  gene expression.
          Default is ``both'' (positive or negative). Can also  be set
          to ``positive'' or ``negative''.

_D_e_t_a_i_l_s:

     'pamr.train' fits a nearest shrunken centroid classifier to gene
     expression data. Details may be found in the PNAS paper referenced
     below. One feature not described there is "heterogeneity
     analysis". Suppose there are two classes labelled "A" and "B".
     CLass "A" is considered a normal class, and "B" an abnormal class.
     Setting hetero="A" transforms   expression values x[i,j] to
     |x[i,j]- mean(x[i,j])| where the mean is taken only over samples
     in class "A". The transformed feature values are then used in Pam.
     This is useful when the abnormal class "B" is heterogeneous, i.e.
     a given gene might have higher expresion than normal for some
     class "B" samples, and lower for others. With more than 2 classes,
     each class is centered on the class specified by hetero.

_V_a_l_u_e:

     A list with components 

       y: The outcome classes.

    yhat: A matrix of predicted classes, each column representing the
          results from one threshold.

    prob: A array of predicted class probabilities. of dimension n by
          nclass by n.threshold. n is the number samples, nclass is the
          number of classes, n.threshold is the number of thresholds
          tried

centroids: A matrix of (unshrunken) class centroids, n by nclass

  hetero: Value of hetero used in call

norm.cent: Centroid of "normal group, if hetero was specified

centroid.overall: 

      sd: A vector of the standard deviations for each gene

threshold: 

 nonzero: A vector of the number of genes that survived the
          thresholding, for each threshold value tried

threshold.scale: A vector of threshold scale factors that were used

se.scale: A vector of standard error scale factors that were used

    call: The calling sequence used

   prior: The prior probabilities used

  errors: The number of trainin errors for each threshold value

_A_u_t_h_o_r(_s):

     Trevor Hastie,Robert Tibshirani, Balasubramanian Narasimhan, and
     Gilbert Chu

_R_e_f_e_r_e_n_c_e_s:

     Robert Tibshirani, Trevor Hastie, Balasubramanian Narasimhan, and
     Gilbert Chu  Diagnosis of multiple cancer types by shrunken
     centroids of gene expression  PNAS 99: 6567-6572.   Available at
     www.pnas.org

_E_x_a_m_p_l_e_s:

     set.seed(120)
     #generate some data
     x <- matrix(rnorm(1000*20),ncol=20)
     y <- sample(c(1:4),size=20,replace=TRUE)
     mydata <- list(x=x,y=factor(y))

     #run classifier
     results<-   pamr.train(mydata)

     # run classifier on all  data except class 4
     results2 <- pamr.train(mydata,sample.subset=(mydata$y!=4))
      
     # run classifier on  only the first 500 genes
     results3 <- pamr.train(mydata,gene.subset=1:500)

