Creating a histogram from a subset created from the subset function - r

Question

This is how I've retrieved my dataset, everything is good so far.
> mantis<-read.csv("mantis.csv")
> attach(mantis)
The dataset provides numerical data on body mass/length/claw strength/etc. of FEMALE and MALE mantises. The object is to create a histogram showing the body masses of ONLY female mantises. I created a subset;
> mantis_sub<-subset(mantis, Sex=="f",select="Body.Mass.g")
Then I tried;
> hist(mantis_sub)
Error in hist.default(mantis_sub) : 'x' must be numeric
I've searched this link;
Plot a histogram of subset of a data
...and I cannot figure out how to properly create this histogram. I am unfortunately not fluent enough in R to understand the solution and the textbook I'm using does not cover this.

Answer 1

It is because mantis_sub is a dataframe (ie a table of body masses, lengths, claw strengths, ..), not a set of numbers, so hist is unsure which column you wish to plot.
You need to extract the column you want to do a histogram of. To do this you put mantis_sub${column name}. The dollar sign extracts the appropriate column from the mantis_sub table.
e.g. to do a histogram of the column named "BodyMass"
hist(mantis_sub$BodyMass)
If you want to do histograms of many columns automatically, then you'll have to loop through them, e.g.
for (column in c("BodyMass", "ClawStrength")) {
hist(mantis_sub[[column]])
}