My expression data frame pretty small subset of it is as such 
 
      gene                    value_1                   value_2
    XLOC_000060           3.662330                   0.3350140
    XLOC_000074           2.568130                   0.0426299


I been struggling with ggplot how to trasform the data so that I can plot it in ggplot i basically how do I define the factor etc.

saw few examples but I guess im still not able to replicate what they did with the sample data 

I end up getting this error `Error in eval(expr, envir, enclos)`  its a pretty fundamental error I suppose which I fail to figure out..

Any help would be highly appreciated  
You have to *tidy* your data to plot it effectively with `ggplot2`. There are many ways to do this, below I show two (assuming you want to plot a heatmap). Note the difference in data rearrangement between `d` and `dd`. Also, highly recommend reading the [tidyr vignette][1] and the *Tidy data* section in the book *"R for data science"* by [Hadley Wickham][2] (creator of ggplot2, tidyr and reshape2). The online version of this book is available [here][3].

    # create sample (untidy) dataset.
    d <- read.table(header = TRUE, text = 
     "gene                   value_1                     value_2
      XLOC_000060           3.662330                   0.3350140
      XLOC_000074           2.568130                   0.0426299")
    
    d
             gene value_1   value_2
    1 XLOC_000060 3.66233 0.3350140
    2 XLOC_000074 2.56813 0.0426299
    
    # tidy it using tidyr package.
    library(tidyr)
    dd <- d %>% gather(sample, value, -gene)
    dd
             gene  sample     value
    1 XLOC_000060 value_1 3.6623300
    2 XLOC_000074 value_1 2.5681300
    3 XLOC_000060 value_2 0.3350140
    4 XLOC_000074 value_2 0.0426299
    
    # plot heatmap.
    ggplot(dd, aes(x = sample, y = gene, fill = value)) + geom_tile()
    
    # tidy it using reshape2 package.
    library(reshape2)
    dd <- melt(d, variable.name = "sample")
    ggplot(dd, aes(x = sample, y = gene, fill = value)) + geom_tile()


  [1]: https://cran.r-project.org/web/packages/tidyr/vignettes/tidy-data.html
  [2]: http://hadley.nz
  [3]: http://r4ds.had.co.nz